diff --git a/collects/mzlib/deflate.ss b/collects/mzlib/deflate.ss
new file mode 100644
index 0000000..7376f76
--- /dev/null
+++ b/collects/mzlib/deflate.ss
@@ -0,0 +1,2206 @@
+#|
+/* deflate.c -- compress data using the deflation algorithm
+ * Copyright (C) 1992-1993 Jean-loup Gailly
+ * This is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License, see the file COPYING.
+ */
+|#
+; Taken from the gzip source distribution
+; Translated directly from C (obviously) by Matthew, July 2000
+
+(invoke-unit/sig
+(let-macro INSERT_STRING (lambda (s match_head)
+			   `(begin
+			      (UPDATE_HASH (gzvector-ref window (+ ,s MIN_MATCH -1)))
+			      (let ([mh (gzvector-ref head ins_h)])
+				(set! ,match_head mh)
+				(gzvector-set! prev (bitwise-and ,s  WMASK) mh))
+			      (gzvector-set! head ins_h ,s)))
+(let-macro pqremove (lambda (tree top)
+		      `(begin
+			 (set! ,top (vector-ref heap SMALLEST))
+			 (vector-set! heap SMALLEST (vector-ref heap heap_len))
+			 (set! heap_len (sub1 heap_len))
+			 (pqdownheap ,tree SMALLEST)))
+(unit/sig ()
+  (import)
+
+  (define (for start < end next proc)
+    (let loop ([n start])
+      (when (< n end)
+	(proc n)
+	(loop (next n)))))
+
+  (define-struct gzvector (vector offset))
+  (define (gzvector-ref v o)
+    (vector-ref (gzvector-vector v)
+		(+ (gzvector-offset v) o)))
+  (define (gzvector-set! v o x)
+    (vector-set! (gzvector-vector v)
+		 (+ (gzvector-offset v) o)
+		 x))
+  (define (gzvector+ v o)
+    (make-gzvector (gzvector-vector v)
+		   (+ (gzvector-offset v) o)))
+
+  (define (gzvector<vec v1 v2)
+    (< (gzvector-offset v1) (gzvector-offset v2)))
+  (define (gzvector-vec v1 v2)
+    (- (gzvector-offset v1) (gzvector-offset v2)))
+
+  (define (gzvector-copy v1 v2 n)
+    (for 0 < n add1
+	 (lambda (m)
+	   (gzvector-set! v2 m (gzvector-ref v1 m)))))
+         
+  (define (gzvector-zero! v n)
+    (for 0 < n add1
+	 (lambda (m)
+	   (gzvector-set! v m 0))))
+
+  (define (Trace stderr str . args)
+    '(apply fprintf (current-error-port) str args))
+  (define Tracevv Trace)
+  (define Tracev Trace)
+  (define (Tracec test . args)
+    (when test
+      (apply Trace args)))
+  (define Tracecv Tracec)
+  (define stderr 'sdterr)
+  
+#|
+/*
+ *  PURPOSE
+ *
+ *      Identify new text as repetitions of old text within a fixed-
+ *      length sliding window trailing behind the new text.
+ *
+ *  DISCUSSION
+ *
+ *      The "deflation" process depends on being able to identify portions
+ *      of the input text which are identical to earlier input (within a
+ *      sliding window trailing behind the input currently being processed).
+ *
+ *      The most straightforward technique turns out to be the fastest for
+ *      most input files: try all possible matches and select the longest.
+ *      The key feature of this algorithm is that insertions into the string
+ *      dictionary are very simple and thus fast, and deletions are avoided
+ *      completely. Insertions are performed at each input character, whereas
+ *      string matches are performed only when the previous match ends. So it
+ *      is preferable to spend more time in matches to allow very fast string
+ *      insertions and avoid deletions. The matching algorithm for small
+ *      strings is inspired from that of Rabin & Karp. A brute force approach
+ *      is used to find longer strings when a small match has been found.
+ *      A similar algorithm is used in comic (by Jan-Mark Wams) and freeze
+ *      (by Leonid Broukhis).
+ *         A previous version of this file used a more sophisticated algorithm
+ *      (by Fiala and Greene) which is guaranteed to run in linear amortized
+ *      time, but has a larger average cost, uses more memory and is patented.
+ *      However the F&G algorithm may be faster for some highly redundant
+ *      files if the parameter max_chain_length (described below) is too large.
+ *
+ *  ACKNOWLEDGEMENTS
+ *
+ *      The idea of lazy evaluation of matches is due to Jan-Mark Wams, and
+ *      I found it in 'freeze' written by Leonid Broukhis.
+ *      Thanks to many info-zippers for bug reports and testing.
+ *
+ *  REFERENCES
+ *
+ *      APPNOTE.TXT documentation file in PKZIP 1.93a distribution.
+ *
+ *      A description of the Rabin and Karp algorithm is given in the book
+ *         "Algorithms" by R. Sedgewick, Addison-Wesley, p252.
+ *
+ *      Fiala,E.R., and Greene,D.H.
+ *         Data Compression with Finite Windows, Comm.ACM, 32,4 (1989) 490-595
+ *
+ *  INTERFACE
+ *
+ *      void lm_init (int pack_level, ush *flags)
+ *          Initialize the "longest match" routines for a new file
+ *
+ *      ulg deflate (void)
+ *          Processes a new input file and return its compressed length. Sets
+ *          the compressed length, crc, deflate flags and internal file
+ *          attributes.
+ */
+
+|#
+
+(define LEVEL 6)
+
+(define OUTBUFSIZ  #x8000);;   /* output buffer size */
+(define INBUFSIZ  #x8000);;   /* input buffer size */
+(define INBUF_EXTRA  64)
+
+(define WSIZE #x8000) ;; /* window size--must be a power of two, and */
+;;                       /*  at least 32K for zip's deflate method */
+
+(define MIN_MATCH  3)
+(define MAX_MATCH  258)
+;; /* The minimum and maximum match lengths */
+
+(define MIN_LOOKAHEAD (+ MAX_MATCH MIN_MATCH 1))
+;; /* Minimum amount of lookahead, except at the end of the input file.
+;;  * See for comments about the MIN_MATCH+1.
+;; */
+
+(define MAX_DIST  (- WSIZE MIN_LOOKAHEAD))
+;; /* In order to simplify the code, particularly on 16 bit machines, match
+;;  * distances are limited to MAX_DIST instead of WSIZE.
+;;  */
+
+(define HASH_BITS  15)
+(define BITS 16)
+
+(define << arithmetic-shift)
+(define (>> x y) (arithmetic-shift x (- y)))
+(define EOF-const -1)
+
+;; /* To save space (see unlzw.c), we overlay prev+head with tab_prefix and
+;;  * window with tab_suffix. Check that we can do this:
+;;  */
+(when (> (<< WSIZE 1) (<< 1 BITS))
+  (error "cannot overlay window with tab_suffix and prev with tab_prefix0"))
+(when (> HASH_BITS (- BITS 1))
+  (error "cannot overlay head with tab_prefix1"))
+
+(define HASH_SIZE (<< 1 HASH_BITS))
+(define HASH_MASK (- HASH_SIZE 1))
+(define WMASK     (- WSIZE 1))
+;; /* HASH_SIZE and WSIZE must be powers of two */
+
+(define NIL 0)
+;; /* Tail of hash chains */
+
+(define FAST 4)
+(define SLOW 2)
+;; /* speed options for the general purpose bit flag */
+
+(define TOO_FAR 4096)
+;; /* Matches of length 3 are discarded if their distance exceeds TOO_FAR */
+
+(define bits_sent 0)
+(define (isgraph c) #t)
+
+;; /* ===========================================================================
+;;  * Local data used by the "longest match" routines.
+;;  */
+
+(define real-table (make-vector (<< 1 BITS) 0))
+
+(define tab_prefix (make-gzvector real-table 0))
+(define prev (make-gzvector real-table 0))
+(define head (make-gzvector real-table WSIZE))
+
+;;  /* DECLARE(uch, window, 2L*WSIZE); */
+;;  /* Sliding window. Input bytes are read into the second half of the window,
+;;   * and move to the first half later to keep a dictionary of at least WSIZE
+;;   * bytes. With this organization, matches are limited to a distance of
+;;   * WSIZE-MAX_MATCH bytes, but this ensures that IO is always
+;;   * performed with a length multiple of the block size. Also, it limits
+;;   * the window size to 64K, which is quite useful on MSDOS.
+;;   * To do: limit the window size to WSIZE+BSZ if SMALL_MEM (the code would
+;;   * be less efficient).
+;;   */
+
+;;  /* DECLARE(Pos, prev, WSIZE); */
+;;  /* Link to older string with same hash index. To limit the size of this
+;;   * array to 64K, this link is maintained only for the last 32K strings.
+;;   * An index in this array is thus a window index modulo 32K.
+;;   */
+
+;;  /* DECLARE(Pos, head, 1<<HASH_BITS); */
+;;  /* Heads of the hash chains or NIL. */
+
+(define window_size (* 2 WSIZE))
+;;  /* window size, 2*WSIZE 
+;;   */
+(define window (make-gzvector (make-vector window_size 0) 0))
+
+(define block_start 0)
+;;  /* window position at the beginning of the current output block. Gets
+;;   * negative when the window is moved backwards.
+;;   */
+
+(define ins_h 0) ;; /* hash index of string to be inserted */
+
+(define H_SHIFT  (quotient (+ HASH_BITS MIN_MATCH -1) MIN_MATCH))
+;; /* Number of bits by which ins_h and del_h must be shifted at each
+;;  * input step. It must be such that after MIN_MATCH steps, the oldest
+;;  * byte no longer takes part in the hash key, that is:
+;;  *   H_SHIFT * MIN_MATCH >= HASH_BITS
+;;  */
+
+(define prev_length 0)
+;; /* Length of the best match at previous step. Matches not greater than this
+;;  * are discarded. This is used in the lazy match evaluation.
+;; */
+
+(define strstart 0)    ;; /* start of string to insert */
+(define match_start 0) ;; /* start of matching string */
+(define eofile #f)     ;; /* flag set at end of input file */
+(define lookahead 0)   ;; /* number of valid bytes ahead in window */
+
+(define max_chain_length 0)
+;; /* To speed up deflation, hash chains are never searched beyond this length.
+;;  * A higher limit improves compression ratio but degrades the speed.
+;;  */
+
+(define max_lazy_match 0)
+;; /* Attempt to find a better match only when the current match is strictly
+;;  * smaller than this value. This mechanism is used only for compression
+;;  * levels >= 4.
+;;  */
+
+(define (max_insert_length)  max_lazy_match)
+;; /* Insert new strings in the hash table only if the match length
+;;  * is not greater than this length. This saves time but degrades compression.
+;;  * max_insert_length is used only for compression levels <= 3.
+;;  */
+
+(define good_match 0)
+;; /* Use a faster search when the previous match is longer than this */
+
+
+;; /* Values for max_lazy_match, good_match and max_chain_length, depending on
+;;  * the desired pack level (0..9). The values given below have been tuned to
+;;  * exclude worst case performance for pathological files. Better values may be
+;;  * found for specific files.
+;;  */
+
+(define-struct config
+  (good_length ;; /* reduce lazy search above this match length */
+   max_lazy    ;; /* do not perform lazy search above this match length */
+   nice_length ;; /* quit search above this match length */
+   max_chain))
+
+(define nice_match MAX_MATCH)
+;; /* Stop searching when current match exceeds this */
+
+(define configuration_table
+  (vector
+   ;; /* good lazy nice chain */
+   (make-config 0 0 0 0)           ;; /* 0 - store only */
+   (make-config 4 4 8 4)           ;; /* 1 - maximum speed, no lazy matches */
+   (make-config 4 5 16 8)          ;; /* 2 */
+   (make-config 4 6 32 32)         ;; /* 3 */
+
+   (make-config 4 4 16 16)         ;; /* 4 - lazy matches */
+   (make-config 8 16 32 32)        ;; /* 5 */
+   (make-config 8 16 128 128)      ;; /* 6 */
+   (make-config 8 32 128 256)      ;; /* 7 */
+   (make-config 32 128 258 1024)   ;; /* 8 */
+   (make-config 32 258 258 4096))) ;; /* 9 - maximum compression */
+
+;; /* Note: the deflate() code requires max_lazy >= MIN_MATCH and max_chain >= 4
+;;  * For deflate_fast() (levels <= 3) good is ignored and lazy has a different
+;; * meaning.
+;; */
+
+;; /* ===========================================================================
+;;  * Update a hash value with the given input byte
+;;  * IN  assertion: all calls to to UPDATE_HASH are made with consecutive
+;;  *    input characters, so that a running hash key can be computed from the
+;;  *    previous key instead of complete recalculation each time.
+;;  */
+(define (UPDATE_HASH c)
+  (set!  ins_h (bitwise-and (bitwise-xor (<< ins_h H_SHIFT) c) HASH_MASK)))
+
+;; /* ===========================================================================
+;;  * Insert string s in the dictionary and set match_head to the previous head
+;;  * of the hash chain (the most recent string with same hash key). Return
+;;  * the previous length of the hash chain.
+;;  * IN  assertion: all calls to to INSERT_STRING are made with consecutive
+;;  *    input characters and the first MIN_MATCH bytes of s are valid
+;;  *    (except for the last MIN_MATCH-1 bytes of the input file).
+;;  */
+;; (define-macro INSERT_STRING <see above>)
+
+;; /* ===========================================================================
+;;  * Initialize the "longest match" routines for a new file
+;; */
+(define (lm_init pack_level)
+  ;; int pack_level; /* 0: store, 1: best speed, 9: best compression */
+
+  (define j 0)
+
+  (when (or (< pack_level 1)
+	    (> pack_level 9))
+    (error "bad pack level"))
+
+  ;; /* Initialize the hash table. */
+  (gzvector-zero! head HASH_SIZE)
+
+  ;; /* prev will be initialized on the fly */
+
+  ;; /* Set the default configuration parameters:
+  ;; */
+  (set! max_lazy_match (config-max_lazy (vector-ref configuration_table pack_level)))
+  (set! good_match (config-good_length (vector-ref configuration_table pack_level)))
+  (set! max_chain_length (config-max_chain (vector-ref configuration_table pack_level)))
+  
+  (let ([flag (cond
+	       [(= pack_level 1) FAST]
+	       [(= pack_level 9) SLOW]
+	       [else 0])])
+    ;; /* ??? reduce max_chain_length for binary files */
+
+    (set! strstart 0)
+    (set! block_start 0)
+
+    (set! lookahead (read_buf window (* 2 WSIZE)))
+
+    (if (or (= lookahead 0) (= lookahead EOF-const))
+	(begin
+	  (set! eofile #t)
+	  (set! lookahead 0))
+	(begin
+	  (set! eofile 0)
+	  ;; /* Make sure that we always have enough lookahead. This is important
+	  ;;  * if input comes from a device such as a tty.
+	  ;;  */
+	  (let loop ()
+	    (when (and (< lookahead MIN_LOOKAHEAD)
+		       (not eofile))
+	      (fill_window)))
+
+	  (set! ins_h 0)
+	  (for 0 < (- MIN_MATCH 1) add1
+	       (lambda (j) (UPDATE_HASH (gzvector-ref window j))))
+	  (Trace stderr "hash init: ~a~n" ins_h)
+	  ;; /* If lookahead < MIN_MATCH, ins_h is garbage, but this is
+	  ;;  * not important since only literal bytes will be emitted.
+	  ;;  */
+	  ))
+
+    flag))
+
+;; /* ===========================================================================
+;;  * Set match_start to the longest match starting at the given string and
+;;  * return its length. Matches shorter or equal to prev_length are discarded,
+;;  * in which case the result is equal to prev_length and match_start is
+;;  * garbage.
+;;  * IN assertions: cur_match is the head of the hash chain for the current
+;;  *   string (strstart) and its distance is <= MAX_DIST, and prev_length >= 1
+;;  */
+(define (longest_match cur_match)
+  ;; IPos cur_match; /* current match */
+
+  (define chain_length max_chain_length)   ;;   /* max hash chain length */
+  (define scan (gzvector+ window strstart)) ;;   /* current string */
+  (define match #f) ;; /* matched string */
+  (define len 0) ;; /* length of current match */
+  (define best_len prev_length) ;; /* best match length so far */
+  (define limit (if (> strstart MAX_DIST)
+		    (- strstart MAX_DIST)
+		    NIL))
+  ;; /* Stop when cur_match becomes <= limit. To simplify the code,
+  ;;  * we prevent matches with the string of window index 0.
+  ;;  */
+
+  ;; /* The code is optimized for HASH_BITS >= 8 and MAX_MATCH-2 multiple of 16.
+  ;;  * It is easy to get rid of this optimization if necessary.
+  ;;  */
+  ;; #if HASH_BITS < 8 || MAX_MATCH != 258
+  ;;   error: Code too clever
+  ;; #endif
+
+  (define strend (gzvector+ window (+ strstart MAX_MATCH)))
+  (define scan_end1 (gzvector-ref scan (- best_len 1)))
+  (define scan_end (gzvector-ref scan best_len))
+
+  ;; /* Do not waste too much time if we already have a good match: */
+  (when (>= prev_length good_match)
+    (set! chain_length (>> chain_length 2)))
+      
+  ;; Assert:
+  (unless (<= strstart (- window_size MIN_LOOKAHEAD))
+    (error "insufficient lookahead"))
+
+  (let/ec break
+    (let loop ()
+      (define (continue)
+	(set! cur_match (gzvector-ref prev (bitwise-and cur_match WMASK)))
+	(when (and (> cur_match limit)
+		   (begin
+		     (set! chain_length (sub1 chain_length))
+		     (not (= chain_length 0))))
+	  (loop)))
+
+      ;; Assert
+      (unless (< cur_match strstart)
+	(error "no future"))
+
+      (set! match (gzvector+ window cur_match))
+
+      ;; /* Skip to next match if the match length cannot increase
+      ;;  * or if the match length is less than 2:
+      ;;  */
+
+      (if (or (not (= (gzvector-ref match best_len) scan_end))
+	      (not (= (gzvector-ref match (- best_len 1)) scan_end1))
+	      (not (= (gzvector-ref match 0) (gzvector-ref scan 0)))
+	      (not (= (begin (set! match (gzvector+ match 1))
+			     (gzvector-ref match 0))
+		      (gzvector-ref scan 1))))
+	  (continue)
+
+	  (begin
+	    ;; /* The check at best_len-1 can be removed because it will be made
+	    ;;  * again later. (This heuristic is not always a win.)
+	    ;;  * It is not necessary to compare scan[2] and match[2] since they
+	    ;;  * are always equal when the other bytes match, given that
+	    ;;  * the hash keys are equal and that HASH_BITS >= 8.
+	    ;;  */
+	    (set! scan (gzvector+ scan 2))
+	    (set! match (gzvector+ match 1))
+
+	    ;; /* We check for insufficient lookahead only every 8th comparison;
+	    ;; * the 256th check will be made at strstart+258.
+	    ;; */
+	    (let ([*++scan (lambda ()
+			     (set! scan (gzvector+ scan 1))
+			     (gzvector-ref scan 0))]
+		  [*++match (lambda ()
+			      (set! match (gzvector+ match 1))
+			      (gzvector-ref match 0))])
+	      (let loop2 ()
+		(when (and (= (*++scan) (*++match)) (= (*++scan) (*++match))
+			   (= (*++scan) (*++match)) (= (*++scan) (*++match))
+			   (= (*++scan) (*++match)) (= (*++scan) (*++match))
+			   (= (*++scan) (*++match)) (= (*++scan) (*++match))
+			   (gzvector<vec scan strend))
+		  (loop2))))
+	    
+	    (set! len (- MAX_MATCH (gzvector-vec strend scan)))
+	    (set! scan (gzvector+ strend (- MAX_MATCH)))
+	    (Trace stderr "Match: ~a~n" len)
+
+	    (when (> len best_len)
+	      (set! match_start cur_match)
+	      (set! best_len len)
+	      (when (>= len nice_match)
+		(break))
+
+	      (set! scan_end1 (gzvector-ref scan (- best_len 1)))
+	      (set! scan_end (gzvector-ref scan best_len)))
+
+	    (continue)))))
+
+  best_len)
+
+;; /* ===========================================================================
+;;  * Check that the match at match_start is indeed a match.
+;;  */
+;;
+(define (check_match start match length)
+  #t)
+
+;; /* ===========================================================================
+;;  * Fill the window when the lookahead becomes insufficient.
+;;  * Updates strstart and lookahead, and sets eofile if end of input file.
+;;  * IN assertion: lookahead < MIN_LOOKAHEAD && strstart + lookahead > 0
+;;  * OUT assertions: at least one byte has been read, or eofile is set;
+;;  *    file reads are performed for at least two bytes (required for the
+;;  *    translate_eol option).
+;;  */
+(define (fill_window)
+  (define n 0)
+  (define m 0)
+
+  (define more (- window_size lookahead strstart))
+  ;; /* Amount of free space at the end of the window. */
+
+  ;; /* If the window is almost full and there is insufficient lookahead,
+  ;;  * move the upper half to the lower one to make room in the upper half.
+  ;;  */
+  (when (>= strstart (+ WSIZE MAX_DIST))
+    (gzvector-copy window (gzvector+ window WSIZE) WSIZE)
+    (set! match_start (- match_start WSIZE))
+    (set! strstart (- strstart WSIZE)) ;; /* we now have strstart >= MAX_DIST: */
+
+    (set! block_start (- block_start WSIZE))
+
+    (for 0 < HASH_SIZE add1
+	 (lambda (n)
+	   (set! m (gzvector-ref head n))
+	   (gzvector-set! head n
+			  (if (>= m WSIZE)
+			      (- m WSIZE)
+			      NIL))))
+
+    (for 0 < WSIZE add1
+	 (lambda (n)
+	   (set! m (gzvector-ref prev n))
+	   (gzvector-set! prev n
+			  (if (>= m WSIZE)
+			      (- m WSIZE)
+			      NIL))
+	   ;; /* If n is not on any hash chain, prev[n] is garbage but
+	   ;;  * its value will never be used.
+	   ;;  */
+	   ))
+
+    (set! more (+ more WSIZE)))
+
+  (when (not eofile)
+    (set! n (read_buf (gzvector+ window (+ strstart lookahead)) more))
+    (if (or (= n 0) (= n EOF-const))
+	(set! eofile #t)
+	(set! lookahead (+ lookahead n)))))
+
+;; /* ===========================================================================
+;;  * Flush the current block, with given end-of-file flag.
+;;  * IN assertion: strstart is set to the end of the current match.
+;;  */
+(define (FLUSH-BLOCK eof)
+  (flush_block (if (>= block_start 0)
+		   (gzvector+ window block_start)
+		   null)
+	       (- strstart block_start) 
+	       eof))
+
+;; /* ===========================================================================
+;;  * Same as above, but achieves better compression. We use a lazy
+;;  * evaluation for matches: a match is finally adopted only if there is
+;;  * no better match at the next window position.
+;;  */
+(define (deflate)
+  (define  hash_head 0) ;; /* head of hash chain */
+  (define prev_match 0) ;; /* previous match */
+  (define flush #f) ;; /* set if current block must be flushed */
+  (define match_available #f) ;; /* set if previous match exists */
+  (define match_length (- MIN_MATCH 1)) ;; /* length of best match */
+
+  ;; /* Process the input block. */
+  (let loop ()
+    (when (not (= lookahead 0))
+      (Trace stderr
+	     "prep ~a ~a ~a ~a ~a ~a ~a ~a ~a~n" hash_head prev_length match_length max_lazy_match strstart
+	      ins_h (gzvector-ref window (+ strstart MIN_MATCH -1))
+	      H_SHIFT HASH_MASK)
+
+      ;; /* Insert the string window[strstart .. strstart+2] in the
+      ;;  * dictionary, and set hash_head to the head of the hash chain:
+      ;;  */
+      (INSERT_STRING strstart hash_head)
+
+      (Trace stderr
+	     "inh ~a ~a ~a ~a ~a ~a ~a~n" hash_head prev_length match_length max_lazy_match strstart
+	      ins_h (gzvector-ref window (+ strstart MIN_MATCH -1)))
+
+      ;; /* Find the longest match, discarding those <= prev_length.
+      ;;  */
+      (set! prev_length match_length)
+      (set! prev_match match_start)
+      (set! match_length (- MIN_MATCH 1))
+
+      (when (and (not (= hash_head NIL))
+		 (< prev_length max_lazy_match)
+		 (<= (- strstart hash_head) MAX_DIST))
+	;; /* To simplify the code, we prevent matches with the string
+	;;  * of window index 0 (in particular we have to avoid a match
+	;;  * of the string with itself at the start of the input file).
+	;;  */
+	(set! match_length (longest_match hash_head))
+	(Trace stderr "blip ~a~n" match_length)
+	;; /* longest_match() sets match_start */
+	(when (> match_length lookahead)
+	  (set! match_length lookahead))
+
+	;; /* Ignore a length 3 match if it is too distant: */
+	(when (and (= match_length MIN_MATCH)
+		   (> (- strstart match_start) TOO_FAR))
+	  ;; /* If prev_match is also MIN_MATCH, match_start is garbage
+	  ;;  * but we will ignore the current match anyway.
+	  ;;  */
+	  (set! match_length (sub1 match_length))))
+
+      ;; /* If there was a match at the previous step and the current
+      ;;  * match is not better, output the previous match:
+      ;;  */
+      (cond
+       [(and (>= prev_length MIN_MATCH)
+	     (<= match_length prev_length))
+	(Trace stderr "x1~n")
+
+	(check_match (- strstart 1) prev_match prev_length)
+
+	(set! flush (ct_tally (- strstart 1 prev_match)
+			      (- prev_length MIN_MATCH)))
+
+	;; /* Insert in hash table all strings up to the end of the match.
+	;;  * strstart-1 and strstart are already inserted.
+	;;  */
+	(set! lookahead (- lookahead (- prev_length 1)))
+	(set! prev_length (- prev_length 2))
+	(let loop ()
+	  (set! strstart (add1 strstart))
+	  (INSERT_STRING strstart hash_head)
+	  (Trace stderr
+		 "inhx ~a ~a ~a ~a ~a ~a~n" hash_head prev_length max_lazy_match strstart
+		 ins_h (gzvector-ref window (+ strstart MIN_MATCH -1)))
+	  ;; /* strstart never exceeds WSIZE-MAX_MATCH, so there are
+	  ;;  * always MIN_MATCH bytes ahead. If lookahead < MIN_MATCH
+	  ;;  * these bytes are garbage, but it does not matter since the
+	  ;;  * next lookahead bytes will always be emitted as literals.
+	  ;;  */
+	  (set! prev_length (sub1 prev_length))
+	  (when (not (= prev_length 0))
+	    (loop)))
+	(set! match_available #f)
+	(set! match_length (- MIN_MATCH 1))
+	(set! strstart (add1 strstart))
+	(when flush
+	  (Trace stderr "flush~n")
+	  (FLUSH-BLOCK 0)
+	  (set! block_start strstart))]
+
+       [match_available
+	(Trace stderr "x2~n")
+	;; /* If there was no match at the previous position, output a
+	;;  * single literal. If there was a match but the current match
+	;;  * is longer, truncate the previous match to a single literal.
+	;;  */
+	;; (Tracevv stderr "~c" (integer->char (gzvector-ref window (- strstart 1))))
+	(when (ct_tally 0 (gzvector-ref window (- strstart 1)))
+	  (FLUSH-BLOCK 0)
+	  (set! block_start strstart))
+	(set! strstart (add1 strstart))
+	(set! lookahead (sub1 lookahead))]
+
+       [else
+	(Trace stderr "x3~n")
+	;; /* There is no previous match to compare with, wait for
+	;;  * the next step to decide.
+	;;  */
+	(set! match_available #t)
+	(set! strstart (add1 strstart))
+	(set! lookahead (sub1 lookahead))])
+
+      ;; Assert 
+      (unless (and (<= strstart bytes_in)
+		   (<= lookahead bytes_in))
+	(error "a bit too far"))
+
+      ;; /* Make sure that we always have enough lookahead, except
+      ;;  * at the end of the input file. We need MAX_MATCH bytes
+      ;;  * for the next match, plus MIN_MATCH bytes to insert the
+      ;;   * string following the next match.
+      ;;  */
+      (let loop ()
+	(when (and (< lookahead MIN_LOOKAHEAD)
+		   (not eofile))
+	  (fill_window)
+	  (loop)))
+
+      (loop)))
+
+  (when match_available
+    (ct_tally 0 (gzvector-ref window (- strstart 1))))
+
+  (FLUSH-BLOCK 1)); /* eof */
+
+#|
+/* trees.c -- output deflated data using Huffman coding
+ * Copyright (C) 1992-1993 Jean-loup Gailly
+ * This is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License, see the file COPYING.
+ */
+
+/*
+ *  PURPOSE
+ *
+ *      Encode various sets of source values using variable-length
+ *      binary code trees.
+ *
+ *  DISCUSSION
+ *
+ *      The PKZIP "deflation" process uses several Huffman trees. The more
+ *      common source values are represented by shorter bit sequences.
+ *
+ *      Each code tree is stored in the ZIP file in a compressed form
+ *      which is itself a Huffman encoding of the lengths of
+ *      all the code strings (in ascending order by source values).
+ *      The actual code strings are reconstructed from the lengths in
+ *      the UNZIP process, as described in the "application note"
+ *      (APPNOTE.TXT) distributed as part of PKWARE's PKZIP program.
+ *
+ *  REFERENCES
+ *
+ *      Lynch, Thomas J.
+ *          Data Compression:  Techniques and Applications, pp. 53-55.
+ *          Lifetime Learning Publications, 1985.  ISBN 0-534-03418-7.
+ *
+ *      Storer, James A.
+ *          Data Compression:  Methods and Theory, pp. 49-50.
+ *          Computer Science Press, 1988.  ISBN 0-7167-8156-5.
+ *
+ *      Sedgewick, R.
+ *          Algorithms, p290.
+ *          Addison-Wesley, 1983. ISBN 0-201-06672-6.
+ *
+ *  INTERFACE
+ *
+ *      void ct_init (ush *attr, int *methodp)
+ *          Allocate the match buffer, initialize the various tables and save
+ *          the location of the internal file attribute (ascii/binary) and
+ *          method (DEFLATE/STORE)
+ *
+ *      void ct_tally (int dist, int lc);
+ *          Save the match info and tally the frequency counts.
+ *
+ *      long flush_block (char *buf, ulg stored_len, int eof)
+ *          Determine the best encoding for the current block: dynamic trees,
+ *          static trees or store, and output the encoded block to the zip
+ *          file. Returns the total compressed length for the file so far.
+ *
+ */
+
+|#
+
+;; /* ===========================================================================
+;;  * Constants
+;;  */
+
+(define MAX_BITS 15)
+;; /* All codes must not exceed MAX_BITS bits */
+
+(define MAX_BL_BITS 7)
+;; /* Bit length codes must not exceed MAX_BL_BITS bits */
+
+(define LENGTH_CODES 29)
+;; /* number of length codes, not counting the special END_BLOCK code */
+
+(define LITERALS  256)
+;; /* number of literal bytes 0..255 */
+
+(define END_BLOCK 256)
+;; /* end of block literal code */
+
+(define L_CODES (+ LITERALS 1 LENGTH_CODES))
+;; /* number of Literal or Length codes, including the END_BLOCK code */
+
+(define D_CODES   30)
+;; /* number of distance codes */
+
+(define BL_CODES  19)
+;; /* number of codes used to transfer the bit lengths */
+
+(define extra_lbits ;; /* extra bits for each length code */
+  (vector 0 0 0 0 0 0 0 0 1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4 5 5 5 5 0))
+
+(define extra_dbits ;; /* extra bits for each distance code */
+  (vector 0 0 0 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 11 11 12 12 13 13))
+
+(define extra_blbits ;; /* extra bits for each bit length code */
+  (vector 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 3 7))
+
+(define STORED_BLOCK 0)
+(define STATIC_TREES 1)
+(define DYN_TREES    2)
+;; /* The three kinds of block type */
+
+(define LIT_BUFSIZE  #x4000)
+(define DIST_BUFSIZE LIT_BUFSIZE)
+;; /* Sizes of match buffers for literals/lengths and distances.  There are
+;;  * 4 reasons for limiting LIT_BUFSIZE to 64K:
+;;  *   - frequencies can be kept in 16 bit counters
+;;  *   - if compression is not successful for the first block, all input data is
+;;  *     still in the window so we can still emit a stored block even when input
+;;  *     comes from standard input.  (This can also be done for all blocks if
+;;  *     LIT_BUFSIZE is not greater than 32K.)
+;;  *   - if compression is not successful for a file smaller than 64K, we can
+;;  *     even emit a stored file instead of a stored block (saving 5 bytes).
+;;  *   - creating new Huffman trees less frequently may not provide fast
+;;  *     adaptation to changes in the input data statistics. (Take for
+;;  *     example a binary file with poorly compressible code followed by
+;;  *     a highly compressible string table.) Smaller buffer sizes give
+;;  *     fast adaptation but have of course the overhead of transmitting trees
+;;  *     more frequently.
+;;  *   - I can't count above 4
+;;  * The current code is general and allows DIST_BUFSIZE < LIT_BUFSIZE (to save
+;;  * memory at the expense of compression). Some optimizations would be possible
+;;  * if we rely on DIST_BUFSIZE == LIT_BUFSIZE.
+;;  */
+(when (> LIT_BUFSIZE INBUFSIZ)
+  (error "cannot overlay l_buf and inbuf"))
+
+(define REP_3_6      16)
+;; /* repeat previous bit length 3-6 times (2 bits of repeat count) */
+
+(define REPZ_3_10    17)
+;; /* repeat a zero length 3-10 times  (3 bits of repeat count) */
+
+(define REPZ_11_138  18)
+;; /* repeat a zero length 11-138 times  (7 bits of repeat count) */
+
+;; /* ===========================================================================
+;;  * Local data
+;;  */
+
+;; /* Data structure describing a single value and its code string. */
+(define-struct ct_data (freq code dad len))
+;;    union {
+;;        ush  freq;       ;; /* frequency count */
+;;        ush  code;       ;; /* bit string */
+;;    } fc;
+;;    union {
+;;        ush  dad;        ;; /* father node in Huffman tree */
+;;        ush  len;        ;; /* length of bit string */
+;;    } dl;
+#|
+(define ct_data-freq ct_data-freq/code)
+(define ct_data-code ct_data-freq/code)
+(define ct_data-dad ct_data-dad/len)
+(define ct_data-len ct_data-dad/len)
+
+(define set-ct_data-freq! set-ct_data-freq/code!)
+(define set-ct_data-code! set-ct_data-freq/code!)
+(define set-ct_data-dad! set-ct_data-dad/len!)
+(define set-ct_data-len! set-ct_data-dad/len!)
+|#
+(define _make-ct_data make-ct_data)
+
+(define HEAP_SIZE (+ (* 2 L_CODES) 1))
+;; /* maximum heap size */
+
+(define dyn_ltree (make-vector HEAP_SIZE 'uninit-dl))   ;; /* literal and length tree */
+(define dyn_dtree (make-vector (+ (* 2 D_CODES) 1) 'uninit-dd)) ;; /* distance tree */
+
+(define static_ltree (make-vector (+ L_CODES 2) 'uninit-sl))
+;; /* The static literal tree. Since the bit lengths are imposed, there is no
+;;  * need for the L_CODES extra codes used during heap construction. However
+;;  * The codes 286 and 287 are needed to build a canonical tree (see ct_init
+;;  * below).
+;;  */
+
+(define static_dtree (make-vector D_CODES 'uninit-sd))
+;; /* The static distance tree. (Actually a trivial tree since all codes use
+;;  * 5 bits.)
+;;  */
+
+(define bl_tree (make-vector (+ (* 2 BL_CODES) 1) 'uninit-dl))
+;; /* Huffman tree for the bit lengths */
+
+(define-struct tree_desc
+  (dyn_tree;      ;; /* the dynamic tree */
+   static_tree;   ;; /* corresponding static tree or NULL */
+   extra_bits;    ;; /* extra bits for each code or NULL */
+   extra_base;    ;; /* base index for extra_bits */
+   elems;         ;; /* max number of elements in the tree */
+   max_length;    ;; /* max bit length for the codes */
+   max_code));    ;; /* largest code with non zero frequency */
+
+(define l_desc (make-tree_desc
+		dyn_ltree static_ltree extra_lbits
+		(+ LITERALS 1) L_CODES MAX_BITS 0))
+
+(define d_desc (make-tree_desc
+		dyn_dtree static_dtree extra_dbits
+		0 D_CODES MAX_BITS 0))
+
+(define bl_desc (make-tree_desc
+		 bl_tree #f extra_blbits
+		 0 BL_CODES MAX_BL_BITS 0))
+
+
+(define bl_count (make-vector (+ MAX_BITS 1) 0))
+;; /* number of codes at each bit length for an optimal tree */
+
+(define bl_order 
+  (vector 16 17 18 0 8 7 9 6 10 5 11 4 12 3 13 2 14 1 15))
+;; /* The lengths of the bit length codes are sent in order of decreasing
+;;  * probability, to avoid transmitting the lengths for unused bit length codes.
+;;  */
+
+(define heap (make-vector (+ (* 2 L_CODES) 1) 0)) ;; /* heap used to build the Huffman trees */
+(define heap_len 0)               ;; /* number of elements in the heap */
+(define heap_max 0)               ;; /* element of largest frequency */
+;; /* The sons of heap[n] are heap[2*n] and heap[2*n+1]. heap[0] is not used.
+;;  * The same heap array is used to build all trees.
+;;  */
+
+(define depth (make-vector (+ (* 2 L_CODES) 1) 0))
+;; /* Depth of each subtree used as tie breaker for trees of equal frequency */
+
+(define length_code (make-vector (- MAX_MATCH MIN_MATCH -1) 0))
+;; /* length code for each normalized match length (0 == MIN_MATCH) */
+
+(define dist_code (make-vector 512 0))
+;; /* distance codes. The first 256 values correspond to the distances
+;;  * 3 .. 258, the last 256 values correspond to the top 8 bits of
+;;  * the 15 bit distances.
+;;  */
+
+(define base_length (make-vector LENGTH_CODES 0))
+;; /* First normalized length for each code (0 = MIN_MATCH) */
+
+(define base_dist (make-vector D_CODES 0))
+;; /* First normalized distance for each code (0 = distance of 1) */
+
+(define inbuf (make-gzvector (make-vector (+ INBUFSIZ INBUF_EXTRA) 0) 0))
+(define l_buf inbuf)
+;; /* DECLARE(uch, l_buf, LIT_BUFSIZE);  buffer for literals or lengths */
+
+(define d_buf (make-vector DIST_BUFSIZE 0))
+;; /* DECLARE(ush, d_buf, DIST_BUFSIZE); buffer for distances */
+
+(define flag_buf (make-vector (/ LIT_BUFSIZE 8) 0))
+;; /* flag_buf is a bit array distinguishing literals from lengths in
+;;  * l_buf, thus indicating the presence or absence of a distance.
+;;  */
+
+(define last_lit 0)    ;; /* running index in l_buf */
+(define last_dist 0)   ;; /* running index in d_buf */
+(define last_flags 0)  ;; /* running index in flag_buf */
+(define flags 0)            ;; /* current flags not yet saved in flag_buf */
+(define flag_bit 0)         ;; /* current bit used in flags */
+;; /* bits are filled in flags starting at bit 0 (least significant).
+;;  * Note: these flags are overkill in the current code since we don't
+;;  * take advantage of DIST_BUFSIZE == LIT_BUFSIZE.
+;; */
+
+(define opt_len 0);        ;; /* bit length of current block with optimal trees */
+(define static_len 0);     ;; /* bit length of current block with static trees */
+
+(define compressed_len 0); ;; /* total bit length of compressed file */
+
+(define input_len 0);      ;; /* total byte length of input file */
+;; /* input_len is for debugging only since we can get it by other means. */
+
+;; (define block_start 0);       ;; /* window offset of current block */
+;; (define strstart 0); ;; /* window offset of current string */
+
+(define (send_code c tree) (send_bits (ct_data-code (vector-ref tree c))
+				      (ct_data-len (vector-ref tree c))))
+;; /* Send a code of the given tree. c and tree must not have side effects */
+
+(define (d_code dist) 
+  (if (< dist 256)
+      (vector-ref dist_code dist)
+      (vector-ref dist_code (+ 256 (>> dist 7)))))
+;; /* Mapping from a distance to a distance code. dist is the distance - 1 and
+;;  * must not have side effects. dist_code[256] and dist_code[257] are never
+;;  * used.
+;; */
+
+;; /* ===========================================================================
+;;  * Allocate the match buffer, initialize the various tables and save the
+;;  * location of the internal file attribute (ascii/binary) and method
+;;  * (DEFLATE/STORE).
+;; */
+(define (ct_init)
+
+  (define n 0)        ;; /* iterates over tree elements */
+  (define bits 0)     ;; /* bit counter */
+  (define length 0)   ;; /* length value */
+  (define code 0)     ;; /* code value */
+  (define dist 0)     ;; /* distance index */
+
+  (set! compressed_len 0)
+  (set! input_len 0)
+  
+  (unless (ct_data? (vector-ref static_dtree 0)) ;; /* ct_init already called? */
+    ;; /* Initialize the mapping length (0..255) -> length code (0..28) */
+    (set! length 0)
+    (for 0 < (- LENGTH_CODES 1) add1
+	 (lambda (code)
+	   (vector-set! base_length code length)
+	   (for 0 < (<< 1 (vector-ref extra_lbits code)) add1
+		(lambda (n)
+		  (vector-set! length_code length code)
+		  (set! length (add1 length))))))
+    
+    ;; Assert 
+    (unless (= length 256)
+      (error "ct_init: length != 256"))
+
+    ;; /* Note that the length 255 (match length 258) can be represented
+    ;;  * in two different ways: code 284 + 5 bits or code 285, so we
+    ;;  * overwrite length_code[255] to use the best encoding:
+    ;; */
+    (vector-set! length_code (- length 1) code)
+
+    ;; /* Initialize the mapping dist (0..32K) -> dist code (0..29) */
+    (set! dist 0)
+    (for 0 < 16 add1
+	 (lambda (code)
+	   (vector-set! base_dist code dist)
+	   (for 0 < (<< 1 (vector-ref extra_dbits code)) add1
+		(lambda (n)
+		  (vector-set! dist_code dist code)
+		  (set! dist (add1 dist))))))
+
+    ;; Assert
+    (unless (= dist 256)
+      (error "ct_init: dist != 256"))
+    (set! dist (>> dist 7)) ;; /* from now on, all distances are divided by 128 */
+    (for 16 < D_CODES add1
+	 (lambda (code)
+	   (vector-set! base_dist code (<< dist 7))
+	   (for 0 < (<< 1 (- (vector-ref extra_dbits code) 7)) add1
+		(lambda (n)
+		  (vector-set! dist_code (+ 256 dist) code)
+		  (set! dist (add1 dist))))))
+
+    ;; Assert
+    (unless (= dist 256)
+      (error "ct_init: 256+dist != 512"))
+
+    ;; /* Construct the codes of the static literal tree */
+    (for 0 <= MAX_BITS add1
+	 (lambda (bits)
+	   (vector-set! bl_count bits 0)))
+
+    (let ([init-ltree
+	   (lambda (s e v)
+	     (for s <= e add1
+		  (lambda (n)
+		    (vector-set! static_ltree n (_make-ct_data #f 0 #f v))
+		    (vector-set! bl_count v (add1 (vector-ref bl_count v))))))])
+      (init-ltree 0 143 8)
+      (init-ltree 144 255 9)
+      (init-ltree 256 279 7)
+      (init-ltree 280 287 8))
+    ;; /* Codes 286 and 287 do not exist, but we must include them in the
+    ;;  * tree construction to get a canonical Huffman tree (longest code
+    ;;  * all ones)
+    ;; */
+    (gen_codes static_ltree (+ L_CODES 1))
+
+    ;; /* The static distance tree is trivial: */
+    (for 0 < D_CODES add1
+	 (lambda (n)
+	   (vector-set! static_dtree n 
+			(_make-ct_data #f (bi_reverse n 5)
+				       #f 5))))
+
+    ;; /* Initialize the first block of the first file: */
+    (init_block)))
+
+;; /* ===========================================================================
+;;  * Initialize a new block.
+;; */
+(define inited-once? #f)
+(define (init_block)
+  (for 0 < (if inited-once? L_CODES HEAP_SIZE) add1
+       (lambda (n)
+	 (vector-set! dyn_ltree n (_make-ct_data 0 #f 0 #f))))
+  (for 0 < (if inited-once? D_CODES (+ (* 2 D_CODES) 1)) add1
+       (lambda (n)
+	 (vector-set! dyn_dtree n (_make-ct_data 0 #f 0 #f))))
+  (for 0 < (if inited-once? BL_CODES (+ (* 2 BL_CODES) 1)) add1
+       (lambda (n)
+	 (vector-set! bl_tree n (_make-ct_data 0 #f 0 #f))))
+
+  (set! inited-once? #t)
+
+  (set-ct_data-freq! (vector-ref dyn_ltree END_BLOCK) 1)
+  (set! opt_len 0)
+  (set! static_len 0)
+  (set! last_lit 0)
+  (set! last_dist 0)
+  (set! last_flags 0)
+  (set! flags 0)
+  (set! flag_bit 1))
+
+(define SMALLEST 1)
+;; /* Index within the heap array of least frequent node in the Huffman tree */
+
+
+;; /* ===========================================================================
+;;  * Remove the smallest element from the heap and recreate the heap with
+;;  * one less element. Updates heap and heap_len.
+;; */
+;; (define-macro pqremove <see above>)
+
+;; /* ===========================================================================
+;;  * Compares to subtrees, using the tree depth as tie breaker when
+;;  * the subtrees have equal frequency. This minimizes the worst case length.
+;;  */
+(define (smaller tree n m)
+  (or (< (ct_data-freq (vector-ref tree n)) (ct_data-freq (vector-ref tree m)))
+      (and (= (ct_data-freq (vector-ref tree n)) (ct_data-freq (vector-ref tree m)))
+	   (<= (vector-ref depth n) (vector-ref depth m)))))
+
+;; /* ===========================================================================
+;;  * Restore the heap property by moving down the tree starting at node k,
+;;  * exchanging a node with the smallest of its two sons if necessary, stopping
+;;  * when the heap property is re-established (each father smaller than its
+;;  * two sons).
+;;  */
+(define (pqdownheap tree k)
+  ;; ct_data near *tree;  /* the tree to restore */
+  ;; int k;               /* node to move down */
+
+  (define v (vector-ref heap k))
+  (define j (<< k 1))  ;; /* left son of k */
+  (let/ec break
+    (let loop ()
+      (when (<= j heap_len)
+	;; /* Set j to the smallest of the two sons: */
+	(when (and (< j heap_len)
+		   (smaller tree 
+			    (vector-ref heap (+ j 1))
+			    (vector-ref heap j)))
+	  (set! j (add1 j)))
+	
+	;; /* Exit if v is smaller than both sons */
+	(when (smaller tree  v (vector-ref heap j))
+	  (break))
+
+	;; /* Exchange v with the smallest son */
+	(vector-set! heap k (vector-ref heap j))
+	(set! k j)
+
+	;; /* And continue down the tree, setting j to the left son of k */
+	(set! j (<< j 1))
+
+	(loop))))
+  (vector-set! heap k v))
+
+;; /* ===========================================================================
+;;  * Compute the optimal bit lengths for a tree and update the total bit length
+;;  * for the current block.
+;;  * IN assertion: the fields freq and dad are set, heap[heap_max] and
+;;  *    above are the tree nodes sorted by increasing frequency.
+;;  * OUT assertions: the field len is set to the optimal bit length, the
+;;  *     array bl_count contains the frequencies for each bit length.
+;;  *     The length opt_len is updated; static_len is also updated if stree is
+;;  *     not null.
+;; */
+(define (gen_bitlen desc)
+  ;; tree_desc near *desc; ;; /* the tree descriptor */
+
+  (define tree (tree_desc-dyn_tree desc))
+  (define extra (tree_desc-extra_bits desc))
+  (define base (tree_desc-extra_base desc))
+  (define max_code (tree_desc-max_code desc))
+  (define max_length (tree_desc-max_length desc))
+  (define stree (tree_desc-static_tree desc))
+  (define h 0) ;; /* heap index */
+  (define n 0) (define m 0) ;; /* iterate over the tree elements */
+  (define bits 0)           ;; /* bit length */
+  (define xbits 0)          ;; /* extra bits */
+  (define f 0);              ;; /* frequency */
+  (define overflow 0);   ;; /* number of elements with bit length too large */
+
+  (for 0 <= MAX_BITS add1
+       (lambda (bits)
+	 (vector-set! bl_count bits 0)))
+
+  ;; /* In a first pass, compute the optimal bit lengths (which may
+  ;;  * overflow in the case of the bit length tree).
+  ;;  */
+  (set-ct_data-len! (vector-ref tree (vector-ref heap heap_max)) 0) ;; /* root of the heap */
+
+  (for (+ 1 heap_max) < HEAP_SIZE add1
+       (lambda (h)
+	 (set! n (vector-ref heap h))
+	 (set! bits (+ (ct_data-len (vector-ref tree (ct_data-dad (vector-ref tree n)))) 1))
+	 (when (> bits max_length) 
+	   (set! bits max_length)
+	   (set! overflow (add1 overflow)))
+	 (set-ct_data-len! (vector-ref tree n) bits)
+	 ;; /* We overwrite tree[n].Dad which is no longer needed */
+
+	 (unless (> n max_code)
+	   ;; /* leaf node */
+
+	   (vector-set! bl_count bits (add1 (vector-ref bl_count bits)))
+	   (set! xbits 0)
+	   (when (>= n base)
+	     (set! xbits (vector-ref extra (- n base))))
+	   (set! f (ct_data-freq (vector-ref tree n)))
+	   (set! opt_len (+ opt_len (* f (+ bits xbits))))
+	   (when stree
+	     (set! static_len (+ static_len (* f (+ (ct_data-len (vector-ref stree n)) xbits))))))))
+
+  (unless (= overflow 0)
+
+    (Trace stderr "~nbit length overflow~n")
+    ;; /* This happens for example on obj2 and pic of the Calgary corpus */
+
+    ;; /* Find the first bit length which could increase: */
+    (let loop ()
+      (set! bits (- max_length 1))
+      (let loop ()
+	(when (= (vector-ref bl_count bits) 0)
+	  (set! bits (sub1 bits))
+	  (loop)))
+      (vector-set! bl_count bits (sub1 (vector-ref bl_count bits)))
+      (vector-set! bl_count (+ bits 1) (+ (vector-ref bl_count (+ bits 1)) 2))
+      (vector-set! bl_count max_length (sub1 (vector-ref bl_count max_length)))
+      ;; /* The brother of the overflow item also moves one step up,
+      ;;  * but this does not affect bl_count[max_length]
+      ;;  */
+      (set! overflow (- overflow 2))
+      (when (> overflow 0)
+	(loop)))
+
+    ;; /* Now recompute all bit lengths, scanning in increasing frequency.
+    ;;  * h is still equal to HEAP_SIZE. (It is simpler to reconstruct all
+    ;;  * lengths instead of fixing only the wrong ones. This idea is taken
+    ;;  * from 'ar' written by Haruhiko Okumura.)
+    ;;  */
+    (for max_length > 0 sub1
+	 (lambda (bits)
+	   (set! n (vector-ref bl_count bits))
+	   (let loop ()
+	     (when (not (= n 0))
+	       (set! h (sub1 h))
+	       (set! m (vector-ref heap h))
+	       (if (> m max_code)
+		   (loop)
+		   (begin
+		     (when (not (= (ct_data-len (vector-ref tree m)) bits))
+		       (set! opt_len
+			     (+ opt_len (* (- bits (ct_data-len (vector-ref tree m)))
+					   (ct_data-freq (vector-ref tree m))))))
+		     (set-ct_data-len! (vector-ref tree m) bits)))
+	       (set! n (sub1 n))
+	       (loop)))))))
+
+;; /* ===========================================================================
+;;  * Generate the codes for a given tree and bit counts (which need not be
+;;  * optimal).
+;;  * IN assertion: the array bl_count contains the bit length statistics for
+;;  * the given tree and the field len is set for all tree elements.
+;;  * OUT assertion: the field code is set for all tree elements of non
+;;  *     zero code length.
+;; */
+(define (gen_codes tree max_code)
+  ;; ct_data near *tree;        /* the tree to decorate */
+  ;; int max_code;              /* largest code with non zero frequency */
+
+  (define next_code (make-vector (+ MAX_BITS 1) 0)) ;; /* next code value for each bit length */
+  (define code 0)              ;; /* running code value */
+  (define bits 0)                  ;; /* bit index */
+  (define n 0)                     ;; /* code index */
+
+  ;; /* The distribution counts are first used to generate the code values
+  ;;  * without bit reversal.
+  ;;  */
+  (for 1 <= MAX_BITS add1
+       (lambda (bits)
+	 (set! code (<< (+ code (vector-ref bl_count (- bits 1))) 1))
+	 (vector-set! next_code bits code)))
+  ;; /* Check that the bit counts in bl_count are consistent. The last code
+  ;;  * must be all ones.
+  ;;  */
+  ;; Assert 
+  (unless (= (+ code (vector-ref bl_count MAX_BITS)-1)
+	     (- (<< 1 MAX_BITS) 1))
+    "inconsistent bit counts")
+  (Tracev stderr "\~ngen_codes: max_code ~a " max_code)
+
+  (for  0 <= max_code add1
+	(lambda (n)
+	  (let ([len (ct_data-len (vector-ref tree n))])
+	    (unless (= len 0)
+	      ;; /* Now reverse the bits */
+	      (let ([nc (vector-ref next_code len)])
+		(set-ct_data-code! (vector-ref tree n)
+				   (bi_reverse nc len))
+		(vector-set! next_code len (add1 nc)))
+
+	      (Tracec (not (eq? tree static_ltree))
+		      stderr
+		      "~nn ~a ~c l ~a c ~x (~x) "
+		      n #\space len
+		      (or (ct_data-code (vector-ref tree n)) 0)
+		      (or (- (vector-ref next_code len) 1) 0)))))))
+
+;; /* ===========================================================================
+;;  * Construct one Huffman tree and assigns the code bit strings and lengths.
+;;  * Update the total bit length for the current block.
+;;  * IN assertion: the field freq is set for all tree elements.
+;;  * OUT assertions: the fields len and code are set to the optimal bit length
+;;  *     and corresponding code. The length opt_len is updated; static_len is
+;;  *     also updated if stree is not null. The field max_code is set.
+;;  */
+(define (build_tree desc)
+  ;; tree_desc near *desc; ;; /* the tree descriptor */
+
+  (define tree (tree_desc-dyn_tree desc))
+  (define stree (tree_desc-static_tree desc))
+  (define elems (tree_desc-elems desc))
+  (define n 0) (define m 0)   ;; /* iterate over heap elements */
+  (define max_code -1) ;; /* largest code with non zero frequency */
+  (define node elems)  ;; /* next internal node of the tree */
+
+  ;; /* Construct the initial heap, with least frequent element in
+  ;;  * heap[SMALLEST]. The sons of heap[n] are heap[2*n] and heap[2*n+1].
+  ;;  * heap[0] is not used.
+  ;; */
+  (set! heap_len 0)
+  (set! heap_max HEAP_SIZE)
+
+  (for 0 < elems add1
+       (lambda (n)
+	 (Trace stderr "freq: ~a ~a~n" n (ct_data-freq (vector-ref tree n)))
+	 (if (not (= (ct_data-freq (vector-ref tree n)) 0))
+	     (begin
+	       (set! heap_len (add1 heap_len))
+	       (set! max_code n)
+	       (vector-set! heap heap_len n)
+	       (vector-set! depth n 0))
+	     (set-ct_data-len! (vector-ref tree n) 0))))
+
+  (Trace stderr "Building: ~a ~a ~a~n" elems heap_len max_code)
+
+  ;; /* The pkzip format requires that at least one distance code exists,
+  ;;  * and that at least one bit should be sent even if there is only one
+  ;;  * possible code. So to avoid special checks later on we force at least
+  ;;  * two codes of non zero frequency.
+  ;;  */
+  (let loop ()
+    (when (< heap_len 2)
+      (let ([new (if (< max_code 2)
+		     (begin
+		       (set! max_code (add1 max_code))
+		       max_code)
+		     0)])
+	(set! heap_len (add1 heap_len))
+	(vector-set! heap heap_len new)
+	(set-ct_data-freq! (vector-ref tree new) 1)
+        (vector-set! depth new 0)
+	(set! opt_len (sub1 opt_len))
+	(when stree
+	  (set! static_len (- static_len (ct_data-len (vector-ref stree new)))))
+        ;; /* new is 0 or 1 so it does not have extra bits */
+	(loop))))
+
+  (set-tree_desc-max_code! desc max_code)
+
+  ;; /* The elements heap[heap_len/2+1 .. heap_len] are leaves of the tree,
+  ;;  * establish sub-heaps of increasing lengths:
+  ;;  */
+  (for (quotient heap_len 2) >= 1 sub1
+       (lambda (n)
+	 (pqdownheap tree n)))
+
+  ;; /* Construct the Huffman tree by repeatedly combining the least two
+  ;;  * frequent nodes.
+  ;;  */
+  (let loop ()
+    (pqremove tree n);   ;; /* n = node of least frequency */
+    (set! m (vector-ref heap SMALLEST))  ;; /* m = node of next least frequency */
+
+    (set! heap_max (sub1 heap_max))
+    (vector-set! heap heap_max n) ;; /* keep the nodes sorted by frequency */
+    (set! heap_max (sub1 heap_max))
+    (vector-set! heap heap_max m)
+
+    ;; /* Create a new node father of n and m */
+    (set-ct_data-freq! (vector-ref tree node)
+		       (+ (ct_data-freq (vector-ref tree n))
+			  (ct_data-freq (vector-ref tree m))))
+    (vector-set! depth node (+ (max (vector-ref depth n)
+				    (vector-ref depth m))
+			       1))
+    (set-ct_data-dad! (vector-ref tree n) node)
+    (set-ct_data-dad! (vector-ref tree m) node)
+
+    ;; /* and insert the new node in the heap */
+    (vector-set! heap SMALLEST node)
+    (set! node (add1 node))
+    (pqdownheap tree SMALLEST)
+
+    (when (>= heap_len 2)
+      (loop)))
+
+  (set! heap_max (sub1 heap_max))
+  (vector-set! heap heap_max (vector-ref heap SMALLEST))
+
+  ;; /* At this point, the fields freq and dad are set. We can now
+  ;;  * generate the bit lengths.
+  ;;  */
+  (gen_bitlen desc)
+
+  (Trace stderr "Build: ~a~n" max_code)
+  ;; /* The field len is now set, we can generate the bit codes */
+  (gen_codes tree max_code))
+
+;; /* ===========================================================================
+;;  * Scan a literal or distance tree to determine the frequencies of the codes
+;;  * in the bit length tree. Updates opt_len to take into account the repeat
+;;  * counts. (The contribution of the bit length codes will be added later
+;;  * during the construction of bl_tree.)
+;;  */
+(define (scan_tree tree max_code)
+  ;; ct_data near *tree; ;; /* the tree to be scanned */
+  ;; int max_code;       ;; /* and its largest code of non zero frequency */
+
+  (define n 0)                     ;; /* iterates over all tree elements */
+  (define prevlen -1)          ;; /* last emitted length */
+  (define curlen 0)                ;; /* length of current code */
+  (define nextlen (ct_data-len (vector-ref tree 0))) ;; /* length of next code */
+  (define count 0)             ;; /* repeat count of the current code */
+  (define max_count 7)         ;; /* max repeat count */
+  (define min_count 4)         ;; /* min repeat count */
+
+  (when (= nextlen 0)
+    (set! max_count 138)
+    (set! min_count 3))
+  
+  (set-ct_data-len! (vector-ref tree (+ max_code 1)) #xffff) ;; /* guard */
+
+  (for 0 <= max_code add1
+       (lambda (n)
+	 (let/ec continue
+	   (define (inc-bl_tree-freq which amt)
+	     (set-ct_data-freq! (vector-ref bl_tree which)
+				(+ amt (ct_data-freq 
+					(vector-ref bl_tree which)))))
+
+	   (set! curlen nextlen)
+	   (set! nextlen (ct_data-len (vector-ref tree (+ n 1))))
+	   (set! count (add1 count))
+
+	   (cond
+	    [(and (< count max_count)
+		  (= curlen nextlen))
+	     (continue)]
+	    [(< count min_count)
+	     (inc-bl_tree-freq curlen count)]
+	    [(not (= curlen 0))
+	     (when (not (= curlen prevlen))
+	       (inc-bl_tree-freq curlen 1))
+	     (inc-bl_tree-freq REP_3_6 1)]
+	    [(<= count 10)
+	     (inc-bl_tree-freq REPZ_3_10 1)]
+	    [else
+	     (inc-bl_tree-freq REPZ_11_138 1)])
+
+	   (set! count 0)
+	   (set! prevlen curlen)
+
+	   (cond
+	    [(= nextlen 0)
+	     (set! max_count 138)
+	     (set! min_count 3)]
+	    [(= curlen nextlen)
+	     (set! max_count 6)
+	     (set! min_count 3)]
+	    [else
+	     (set! max_count 7)
+	     (set! min_count 4)])))))
+
+;; /* ===========================================================================
+;;  * Send a literal or distance tree in compressed form, using the codes in
+;;  * bl_tree.
+;;  */
+(define (send_tree tree max_code)
+  ;; ct_data near *tree; ;; /* the tree to be scanned */
+  ;; int max_code;       ;; /* and its largest code of non zero frequency */
+
+  (define n 0)                   ;; /* iterates over all tree elements */
+  (define prevlen -1)          ;; /* last emitted length */
+  (define curlen 0)              ;; /* length of current code */
+  (define nextlen (ct_data-len (vector-ref tree 0))) ;; /* length of next code */
+  (define count 0)             ;; /* repeat count of the current code */
+  (define max_count 7)         ;; /* max repeat count */
+  (define min_count 4)         ;; /* min repeat count */
+
+  ;; /* tree[max_code+1].Len = -1; */  ;; /* guard already set */
+  (when (= nextlen 0) 
+    (set! max_count 138)
+    (set! min_count 3))
+
+  (for 0 <= max_code add1
+       (lambda (n)
+	 (let/ec continue
+	   (set! curlen nextlen)
+	   (set! nextlen (ct_data-len (vector-ref tree (+ n 1))))
+	   
+	   (set! count (add1 count))
+	   (cond
+	    [(and (< count max_count)
+		  (= curlen nextlen))
+	     (continue)]
+	    [(< count min_count)
+	     (let loop ()
+	       (send_code curlen bl_tree)
+	       (set! count (sub1 count))
+	       (when (not (= count 0))
+		 (loop)))]
+	    [(not (= curlen 0))
+	     (when (not (= curlen prevlen))
+	       (send_code curlen bl_tree)
+	       (set! count (sub1 count)))
+	     ;; Assert
+	     (unless (>= 6 count 3)
+	       (error " 3_6?"))
+	     (send_code REP_3_6 bl_tree)
+	     (send_bits (- count 3) 2)]
+	    [(<= count 10)
+	     (send_code REPZ_3_10 bl_tree)
+	     (send_bits (- count 3) 3)]
+	    [else
+	     (send_code REPZ_11_138 bl_tree)
+	     (send_bits (- count 11) 7)])
+
+	   (set! count 0)
+	   (set! prevlen curlen)
+	   
+	   (cond
+	    [(= nextlen 0)
+	     (set! max_count 138)
+	     (set! min_count 3)]
+	    [(= curlen nextlen)
+	     (set! max_count 6)
+	     (set! min_count 3)]
+	    [else
+	     (set! max_count 7)
+	     (set! min_count 4)])))))
+
+;; /* ===========================================================================
+;;  * Construct the Huffman tree for the bit lengths and return the index in
+;;  * bl_order of the last bit length code to send.
+;;  */
+(define (build_bl_tree)
+  (define max_blindex 0)  ;; /* index of last bit length code of non zero freq */
+
+  ;; /* Determine the bit length frequencies for literal and distance trees */
+  (scan_tree dyn_ltree (tree_desc-max_code l_desc))
+  (scan_tree dyn_dtree (tree_desc-max_code d_desc))
+
+  ;; /* Build the bit length tree: */
+  (build_tree bl_desc)
+  ;; /* opt_len now includes the length of the tree representations, except
+  ;;  * the lengths of the bit lengths codes and the 5+5+4 bits for the counts.
+  ;;  */
+
+  ;; /* Determine the number of bit length codes to send. The pkzip format
+  ;;  * requires that at least 4 bit length codes be sent. (appnote.txt says
+  ;;  * 3 but the actual value used is 4.)
+  ;;  */
+  (set! max_blindex (- BL_CODES 1))
+  (let loop ()
+    (when (and (>= max_blindex 3) 
+	       (= (ct_data-len (vector-ref bl_tree
+					   (vector-ref bl_order max_blindex)))
+		  0))
+      (set! max_blindex (sub1 max_blindex))
+      (loop)))
+
+  ;; /* Update opt_len to include the bit length tree and counts */
+  (set! opt_len (+ opt_len (* 3 (+ max_blindex 1)) 5 5 4))
+  (Tracev stderr "~ndyn trees: dyn ~a, stat ~a" opt_len static_len)
+
+  max_blindex)
+
+;; /* ===========================================================================
+;;  * Send the header for a block using dynamic Huffman trees: the counts, the
+;;  * lengths of the bit length codes, the literal tree and the distance tree.
+;;  * IN assertion: lcodes >= 257, dcodes >= 1, blcodes >= 4.
+;;  */
+(define (send_all_trees lcodes dcodes blcodes)
+  ;; int lcodes, dcodes, blcodes; ;; /* number of codes for each tree */
+
+  ;; Assert 
+  (unless (and (>= lcodes 257)
+	       (>= dcodes 1)
+	       (>= blcodes 4))
+    (error "not enough codes"))
+  ;; Assert 
+  (unless (and (<= lcodes L_CODES)
+	       (<= dcodes D_CODES)
+	       (<= blcodes BL_CODES))
+    (error "too many codes ~a(~a) ~a(~a) ~a(~a)"
+	   lcodes L_CODES
+	   dcodes D_CODES
+	   blcodes BL_CODES))
+
+  (Tracev stderr "~nbl counts: ")
+
+  (send_bits (- lcodes 257) 5) ;; /* not +255 as stated in appnote.txt */
+  (send_bits (- dcodes 1) 5)
+  (send_bits (- blcodes 4) 4) ;; /* not -3 as stated in appnote.txt */
+  (for 0 < blcodes add1
+       (lambda (rank)
+	 (Tracev stderr "~nbl code ~a " (vector-ref bl_order rank))
+	 (send_bits (ct_data-len (vector-ref bl_tree (vector-ref bl_order rank))) 
+		    3)))
+  (Tracev stderr "~nbl tree: sent ~a" bits_sent)
+
+  (send_tree dyn_ltree (- lcodes 1)) ;; /* send the literal tree */
+  (Tracev stderr "~nlit tree: sent ~a" bits_sent)
+
+  (send_tree dyn_dtree (- dcodes 1)) ;; /* send the distance tree */
+  (Tracev stderr "~ndist tree: sent ~a" bits_sent))
+
+;; /* ===========================================================================
+;;  * Determine the best encoding for the current block: dynamic trees, static
+;;  * trees or store, and output the encoded block to the zip file. This function
+;;  * returns the total compressed length for the file so far.
+;;  */
+(define (flush_block buf stored_len eof)
+  ;; char *buf;        ;; /* input block, or NULL if too old */
+  ;; ulg stored_len;   ;; /* length of input block */
+  ;; int eof;          ;; /* true if this is the last block for a file */
+
+  (define opt_lenb 0) (define static_lenb 0) ;; /* opt_len and static_len in bytes */
+  (define max_blindex 0)  ;; /* index of last bit length code of non zero freq */
+
+  (vector-set! flag_buf last_flags flags) ;; /* Save the flags for the last 8 items */
+
+  ;; /* Construct the literal and distance trees */
+  (build_tree l_desc)
+  (Tracev stderr "~nlit data: dyn ~a, stat ~a" opt_len static_len)
+
+  (build_tree d_desc)
+  (Tracev stderr "~ndist data: dyn ~a, stat ~a" opt_len static_len)
+  ;; /* At this point, opt_len and static_len are the total bit lengths of
+  ;;  * the compressed block data, excluding the tree representations.
+  ;;  */
+
+  ;; /* Build the bit length tree for the above two trees, and get the index
+  ;;  * in bl_order of the last bit length code to send.
+  ;;  */
+  (set! max_blindex (build_bl_tree))
+
+  ;; /* Determine the best encoding. Compute first the block length in bytes */
+  (set! opt_lenb (>> (+ opt_len 3 7) 3))
+  (set! static_lenb (>> (+ static_len 3 7) 3))
+  (set! input_len (+ input_len stored_len)) ;; /* for debugging only */
+
+  (Trace stderr "~nopt ~a(~a) stat ~a(~a) stored ~a lit ~a dist ~a "
+         opt_lenb opt_len static_lenb static_len stored_len
+         last_lit last_dist)
+
+  (when (<= static_lenb opt_lenb)
+    (set! opt_lenb static_lenb))
+  
+  ;; /* If compression failed and this is the first and last block,
+  ;;  * and if the zip file can be seeked (to rewrite the local header),
+  ;;  * the whole file is transformed into a stored file:
+  ;;  */
+  (cond
+   [(and (<= (+ stored_len 4) opt_lenb)
+	 (not (= buf 0)))
+    ;; /* 4: two words for the lengths */
+
+    ;; /* The test buf != NULL is only necessary if LIT_BUFSIZE > WSIZE.
+    ;;  * Otherwise we can't have processed more than WSIZE input bytes since
+    ;;  * the last block flush, because compression would have been
+    ;;  * successful. If LIT_BUFSIZE <= WSIZE, it is never too late to
+    ;;  * transform a block into a stored block.
+    ;;  */
+    (send_bits (+ (<< STORED_BLOCK 1) eof) 3)  ;; /* send block type */
+    (set! compressed_len (bitwise-and (+ compressed_len 3 7) (bitwise-not 7)))
+    (set! compressed_len (+ compressed_len (<< (+ stored_len 4) 3)))
+    
+    (copy_block buf stored_len #t)] ;; /* with header */
+   [(= static_lenb opt_lenb)
+    (send_bits (+ (<< STATIC_TREES 1) eof) 3)
+    (compress_block static_ltree static_dtree)
+    (set! compressed_len (+ compressed_len 3 static_len))]
+   [else
+    (send_bits (+ (<< DYN_TREES 1) eof) 3)
+    (send_all_trees (+ (tree_desc-max_code l_desc) 1)
+		    (+ (tree_desc-max_code d_desc) 1)
+		    (+ max_blindex 1))
+    (compress_block dyn_ltree dyn_dtree)
+    (set! compressed_len (+ compressed_len 3 opt_len))])
+
+  ;; Assert 
+  ;; (unless (= compressed_len bits_sent)
+  ;;  (error "bad compressed size"))
+  (init_block)
+
+  (when eof
+    ;; Assert 
+    (unless (= input_len bytes_in)
+      (error "bad input size"))
+    (bi_windup)
+    (set! compressed_len   ;; /* align on byte boundary */
+	  (+ compressed_len 7)))
+
+  (Tracev stderr "~ncomprlen ~a(~a) " (>> compressed_len 3)
+	  (- compressed_len (* 7 eof)))
+
+  (>> compressed_len 3))
+
+;; /* ===========================================================================
+;;  * Save the match info and tally the frequency counts. Return true if
+;;  * the current block must be flushed.
+;;  */
+(define (ct_tally dist lc)
+  ;; int dist;  ;; /* distance of matched string */
+  ;; int lc;    ;; /* match length-MIN_MATCH or unmatched char (if dist==0) */
+
+  (gzvector-set! l_buf last_lit lc)
+  (set! last_lit (add1 last_lit))
+  (if (= dist 0)
+      ;; /* lc is the unmatched char */
+      (set-ct_data-freq! (vector-ref dyn_ltree lc)
+			 (add1 (ct_data-freq (vector-ref dyn_ltree lc))))
+      (begin
+        ;; /* Here, lc is the match length - MIN_MATCH */
+	(set! dist (sub1 dist)) ;; /* dist = match distance - 1 */
+	;; Assert
+        (unless (and (< dist MAX_DIST)
+		     (<= lc (- MAX_MATCH MIN_MATCH))
+		     (< (d_code dist) D_CODES))
+	  (error "ct_tally: bad match"))
+
+	(let* ([i (+ (vector-ref length_code lc) LITERALS 1)]
+	       [ct (vector-ref dyn_ltree i)])
+	  (Trace stderr "Set: ~a~n" i)
+	  (set-ct_data-freq! ct (add1 (ct_data-freq ct))))
+	(let ([ct (vector-ref dyn_dtree (d_code dist))])
+	  (set-ct_data-freq! ct (add1 (ct_data-freq ct))))
+	
+	(vector-set! d_buf last_dist dist)
+	(set! last_dist (add1 last_dist))
+	(set! flags (bitwise-ior flags flag_bit))))
+
+  (set! flag_bit (<< flag_bit 1))
+
+  ;; /* Output the flags if they fill a byte: */
+  (when (= (bitwise-and last_lit 7) 0)
+    (vector-set! flag_buf last_flags flags)
+    (set! last_flags (add1 last_flags))
+    (set! flags 0) (set! flag_bit 1))
+
+  (let/ec return
+
+    ;; /* Try to guess if it is profitable to stop the current block here */
+    (when (and (> LEVEL 2) (= (bitwise-and last_lit #xfff) 0))
+      (let ()
+        ;; /* Compute an upper bound for the compressed length */
+        (define out_length (* last_lit 8))
+        (define in_length (- strstart block_start))
+        
+        (for 0 < D_CODES add1
+             (lambda (dcode)
+               (set! out_length (+ out_length 
+                                   (* (ct_data-freq (vector-ref dyn_dtree dcode))
+                                      (+ 5 (vector-ref extra_dbits dcode)))))))
+        (set! out_length (>> out_length 3))
+        (Trace stderr "~nlast_lit ~a, last_dist ~a, in ~a, out ~~~a(~a%) "
+	       last_lit last_dist in_length out_length
+	       (- 100 (/ (* out_length 100) in_length)))
+        (when (and (< last_dist (quotient last_lit 2))
+                   (< out_length (quotient in_length 2)))
+          (return #t))))
+      
+    (or (= last_lit (- LIT_BUFSIZE 1))
+	(= last_dist DIST_BUFSIZE))
+    ;; /* We avoid equality with LIT_BUFSIZE because of wraparound at 64K
+    ;;  * on 16 bit machines and because stored blocks are restricted to
+    ;;  * 64K-1 bytes.
+    ;;  */
+    ))
+
+;; /* ===========================================================================
+;;  * Send the block data compressed using the given Huffman trees
+;;  */
+(define (compress_block ltree dtree)
+  ;; ct_data near *ltree; ;; /* literal tree */
+  ;; ct_data near *dtree; ;; /* distance tree */
+
+  (define dist 0) ;; /* distance of matched string */
+  (define lc 0) ;; /* match length or unmatched char (if dist == 0) */
+  (define lx 0) ;; /* running index in l_buf */
+  (define  dx 0)    ;; /* running index in d_buf */
+  (define fx 0)    ;; /* running index in flag_buf */
+  (define flag 0)       ;; /* current flags */
+  (define code 0)      ;; /* the code to send */
+  (define extra 0) ;; /* number of extra bits to send */
+
+  (when (not (= last_lit 0))
+    (let loop ()
+      (when (= (bitwise-and lx 7) 0)
+	(set! flag (vector-ref flag_buf fx))
+	(set! fx (add1 fx)))
+      
+      (set! lc (gzvector-ref l_buf lx))
+      (set! lx (add1 lx))
+
+      (cond
+       [(= (bitwise-and flag 1) 0)
+	(send_code lc ltree) ;; /* send a literal byte */
+	(Tracecv (isgraph lc) stderr " '~c' " (integer->char lc))]
+       [else
+	;; /* Here, lc is the match length - MIN_MATCH */
+	(set! code (vector-ref length_code lc))
+	(send_code (+ code LITERALS 1) ltree) ;; /* send the length code */
+	(set! extra (vector-ref extra_lbits code))
+	(when (not (= extra 0))
+	  (set! lc (- lc (vector-ref base_length code)))
+	  (send_bits lc extra))        ;; /* send the extra length bits */
+	(set! dist (vector-ref d_buf dx))
+	(set! dx (add1 dx))
+
+	;; /* Here, dist is the match distance - 1 */
+	(set! code (d_code dist))
+	;; Assert 
+	(unless (< code D_CODES)
+	  (error "bad d_code"))
+
+	(send_code code dtree)       ;; /* send the distance code */
+	(set! extra (vector-ref extra_dbits code))
+	(when (not (= extra 0))
+	  (set! dist (- dist (vector-ref base_dist code)))
+	  (send_bits dist extra))])   ;; /* send the extra distance bits */
+      ;; /* literal or match pair ? */
+      (set! flag (>> flag 1))
+      (when (< lx last_lit)
+	(loop))))
+
+  (send_code END_BLOCK ltree))
+
+#|
+/* bits.c -- output variable-length bit strings
+ * Copyright (C) 1992-1993 Jean-loup Gailly
+ * This is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License, see the file COPYING.
+ */
+
+
+/*
+ *  PURPOSE
+ *
+ *      Output variable-length bit strings. Compression can be done
+ *      to a file or to memory. (The latter is not supported in this version.)
+ *
+ *  DISCUSSION
+ *
+ *      The PKZIP "deflate" file format interprets compressed file data
+ *      as a sequence of bits.  Multi-bit strings in the file may cross
+ *      byte boundaries without restriction.
+ *
+ *      The first bit of each byte is the low-order bit.
+ *
+ *      The routines in this file allow a variable-length bit value to
+ *      be output right-to-left (useful for literal values). For
+ *      left-to-right output (useful for code strings from the tree routines),
+ *      the bits must have been reversed first with bi_reverse().
+ *
+ *      For in-memory compression, the compressed bit stream goes directly
+ *      into the requested output buffer. The input data is read in blocks
+ *      by the mem_read() function. The buffer is limited to 64K on 16 bit
+ *      machines.
+ *
+ *  INTERFACE
+ *
+ *      void bi_init (FILE *zipfile)
+ *          Initialize the bit string routines.
+ *
+ *      void send_bits (int value, int length)
+ *          Write out a bit string, taking the source bits right to
+ *          left.
+ *
+ *      int bi_reverse (int value, int length)
+ *          Reverse the bits of a bit string, taking the source bits left to
+ *          right and emitting them right to left.
+ *
+ *      void bi_windup (void)
+ *          Write out any remaining bits in an incomplete byte.
+ *
+ *      void copy_block(char *buf, unsigned len, int header)
+ *          Copy a stored block to the zip file, storing first the length and
+ *          its one's complement if requested.
+ *
+ */
+|#
+
+(define bytes_in 0)
+
+(define bi_buf 0)
+;; /* Output buffer. bits are inserted starting at the bottom (least significant
+;;  * bits).
+;;  */
+
+(define Buf_size (* 8 2))
+;; /* Number of bits used within bi_buf. (bi_buf might be implemented on
+;;  * more than 16 bits on some systems.)
+;;  */
+
+(define bi_valid 0)
+;; /* Number of valid bits in bi_buf.  All bits above the last valid bit
+;;  * are always zero.
+;;  */
+
+;; /* ===========================================================================
+;;  * Initialize the bit string routines.
+;;  */
+(define (bi_init)
+  (set! bi_buf 0)
+  (set! bi_valid 0)
+  (set! bits_sent 0))
+
+
+;; /* ===========================================================================
+;;  * Send a value on a given number of bits.
+;;  * IN assertion: length <= 16 and value fits in length bits.
+;;  */
+(define (send_bits value length)
+  ;; int value;  /* value to send */
+  ;; int length; /* number of bits */
+
+  (Tracev stderr " l ~a v ~x " length value)
+  ;; Assert
+  (unless (and (> length 0) (<= length 15))
+    (error "invalid length"))
+  (set! bits_sent (+ bits_sent length))
+
+  ;; /* If not enough room in bi_buf, use (valid) bits from bi_buf and
+  ;;  * (16 - bi_valid) bits from value, leaving (width - (16-bi_valid))
+  ;;  * unused bits in value.
+  ;;  */
+  (if (> bi_valid (- Buf_size length))
+      (begin
+        (set! bi_buf (bitwise-ior bi_buf (<< value bi_valid)))
+        (put_short bi_buf)
+        (set! bi_buf (>> value (- Buf_size bi_valid)))
+        (set! bi_valid (+ bi_valid (- length Buf_size))))
+      (begin
+        (set! bi_buf (bitwise-ior bi_buf (<< value bi_valid)))
+        (set! bi_valid (+ bi_valid length)))))
+
+;; /* ===========================================================================
+;;  * Reverse the first len bits of a code, using straightforward code (a faster
+;;  * method would use a table)
+;;  * IN assertion: 1 <= len <= 15
+;;  */
+(define (bi_reverse code len)
+  ;; unsigned code; /* the value to invert */
+  ;; int len;       /* its bit length */
+
+  (let loop ([res 0][code code][len len])
+    (let ([res (<< (bitwise-ior res (bitwise-and code 1)) 1)])
+      (if (> len 1)
+	  (loop res (>> code 1) (sub1 len))
+	  (>> res 1)))))
+
+;; /* ===========================================================================
+;;  * Write out any remaining bits in an incomplete byte.
+;;  */
+(define (bi_windup)
+  (cond
+   [(> bi_valid 8)
+    (put_short bi_buf)]
+   [(> bi_valid 0)
+    (put_byte bi_buf)])
+  (set! bi_buf 0)
+  (set! bi_valid 0)
+  (set! bits_sent (bitwise-and (+ bits_sent 7) (bitwise-not 7))))
+
+;; /* ===========================================================================
+;;  * Run a set of bytes through the crc shift register.  If s is a NULL
+;;  * pointer, then initialize the crc shift register contents instead.
+;;  */
+(define crc 0)
+(define (updcrc s n)
+  ;; uch *s;                 /* pointer to bytes to pump through */
+  ;; unsigned n;             /* number of bytes in s[] */
+
+  (if s
+      (let loop ([c crc][p 0])
+	(if (= p n)
+	    (set! crc c)
+	    (loop (bitwise-xor
+		   (vector-ref crc_32_tab
+			       (bitwise-and
+				(bitwise-xor c (gzvector-ref s p))
+				#xff))
+		   (>> c 8))
+		  (add1 p))))
+      (set! crc #xffffffff)))
+
+(define crc_32_tab
+   #(#x00000000 
+     #x77073096 #xee0e612c #x990951ba #x076dc419
+     #x706af48f #xe963a535 #x9e6495a3 #x0edb8832 #x79dcb8a4
+     #xe0d5e91e #x97d2d988 #x09b64c2b #x7eb17cbd #xe7b82d07
+     #x90bf1d91 #x1db71064 #x6ab020f2 #xf3b97148 #x84be41de
+     #x1adad47d #x6ddde4eb #xf4d4b551 #x83d385c7 #x136c9856
+     #x646ba8c0 #xfd62f97a #x8a65c9ec #x14015c4f #x63066cd9
+     #xfa0f3d63 #x8d080df5 #x3b6e20c8 #x4c69105e #xd56041e4
+     #xa2677172 #x3c03e4d1 #x4b04d447 #xd20d85fd #xa50ab56b
+     #x35b5a8fa #x42b2986c #xdbbbc9d6 #xacbcf940 #x32d86ce3
+     #x45df5c75 #xdcd60dcf #xabd13d59 #x26d930ac #x51de003a
+     #xc8d75180 #xbfd06116 #x21b4f4b5 #x56b3c423 #xcfba9599
+     #xb8bda50f #x2802b89e #x5f058808 #xc60cd9b2 #xb10be924
+     #x2f6f7c87 #x58684c11 #xc1611dab #xb6662d3d #x76dc4190
+     #x01db7106 #x98d220bc #xefd5102a #x71b18589 #x06b6b51f
+     #x9fbfe4a5 #xe8b8d433 #x7807c9a2 #x0f00f934 #x9609a88e
+     #xe10e9818 #x7f6a0dbb #x086d3d2d #x91646c97 #xe6635c01
+     #x6b6b51f4 #x1c6c6162 #x856530d8 #xf262004e #x6c0695ed
+     #x1b01a57b #x8208f4c1 #xf50fc457 #x65b0d9c6 #x12b7e950
+     #x8bbeb8ea #xfcb9887c #x62dd1ddf #x15da2d49 #x8cd37cf3
+     #xfbd44c65 #x4db26158 #x3ab551ce #xa3bc0074 #xd4bb30e2
+     #x4adfa541 #x3dd895d7 #xa4d1c46d #xd3d6f4fb #x4369e96a
+     #x346ed9fc #xad678846 #xda60b8d0 #x44042d73 #x33031de5
+     #xaa0a4c5f #xdd0d7cc9 #x5005713c #x270241aa #xbe0b1010
+     #xc90c2086 #x5768b525 #x206f85b3 #xb966d409 #xce61e49f
+     #x5edef90e #x29d9c998 #xb0d09822 #xc7d7a8b4 #x59b33d17
+     #x2eb40d81 #xb7bd5c3b #xc0ba6cad #xedb88320 #x9abfb3b6
+     #x03b6e20c #x74b1d29a #xead54739 #x9dd277af #x04db2615
+     #x73dc1683 #xe3630b12 #x94643b84 #x0d6d6a3e #x7a6a5aa8
+     #xe40ecf0b #x9309ff9d #x0a00ae27 #x7d079eb1 #xf00f9344
+     #x8708a3d2 #x1e01f268 #x6906c2fe #xf762575d #x806567cb
+     #x196c3671 #x6e6b06e7 #xfed41b76 #x89d32be0 #x10da7a5a
+     #x67dd4acc #xf9b9df6f #x8ebeeff9 #x17b7be43 #x60b08ed5
+     #xd6d6a3e8 #xa1d1937e #x38d8c2c4 #x4fdff252 #xd1bb67f1
+     #xa6bc5767 #x3fb506dd #x48b2364b #xd80d2bda #xaf0a1b4c
+     #x36034af6 #x41047a60 #xdf60efc3 #xa867df55 #x316e8eef
+     #x4669be79 #xcb61b38c #xbc66831a #x256fd2a0 #x5268e236
+     #xcc0c7795 #xbb0b4703 #x220216b9 #x5505262f #xc5ba3bbe
+     #xb2bd0b28 #x2bb45a92 #x5cb36a04 #xc2d7ffa7 #xb5d0cf31
+     #x2cd99e8b #x5bdeae1d #x9b64c2b0 #xec63f226 #x756aa39c
+     #x026d930a #x9c0906a9 #xeb0e363f #x72076785 #x05005713
+     #x95bf4a82 #xe2b87a14 #x7bb12bae #x0cb61b38 #x92d28e9b
+     #xe5d5be0d #x7cdcefb7 #x0bdbdf21 #x86d3d2d4 #xf1d4e242
+     #x68ddb3f8 #x1fda836e #x81be16cd #xf6b9265b #x6fb077e1
+     #x18b74777 #x88085ae6 #xff0f6a70 #x66063bca #x11010b5c
+     #x8f659eff #xf862ae69 #x616bffd3 #x166ccf45 #xa00ae278
+     #xd70dd2ee #x4e048354 #x3903b3c2 #xa7672661 #xd06016f7
+     #x4969474d #x3e6e77db #xaed16a4a #xd9d65adc #x40df0b66
+     #x37d83bf0 #xa9bcae53 #xdebb9ec5 #x47b2cf7f #x30b5ffe9
+     #xbdbdf21c #xcabac28a #x53b39330 #x24b4a3a6 #xbad03605
+     #xcdd70693 #x54de5729 #x23d967bf #xb3667a2e #xc4614ab8
+     #x5d681b02 #x2a6f2b94 #xb40bbe37 #xc30c8ea1 #x5a05df1b
+     #x2d02ef8d))
+
+;; /* ===========================================================================
+;;  * Copy a stored block to the zip file, storing first the length and its
+;;  * one's complement if requested.
+;; */
+(define (copy_block buf len header)
+  ;; char     *buf;    /* the input data */
+  ;; unsigned len;     /* its length */
+  ;; int      header;  /* true if block header must be written */
+
+  (bi_windup);; /* align on byte boundary */
+
+  (when header
+    (put_short len)
+    (put_short (bitwise-not len))
+    (set! bits_sent (+ bits_sent (* 2 16))))
+
+  (set! bits_sent (+ bits_sent (<< len 3)))
+
+  (let loop ([len len][pos 0])
+    (unless (zero? len)
+      (put_byte (gzvector-ref buf pos))
+      (loop (add1 pos)))))
+
+;; /* ===========================================================================
+;;  * Read a new buffer from the current input file, perform end-of-line
+;;  * translation, and update the crc and input file size.
+;;  * IN assertion: size >= 2 (for end-of-line translation)
+;;  */
+(define (read_buf buf size)
+  ;; char *buf;
+  ;; unsigned size;
+
+  ;; Assert
+  ;; (unless (= insize 0)
+  ;;   (error "inbuf not empty"))
+
+  (let* ([s (read-string size ifd)]
+	 [len (if (eof-object? s)
+		  EOF-const
+		  (string-length s))])
+    (when (positive? len)
+      (let loop ([l (string->list s)][p 0])
+	(unless (null? l)
+	  (gzvector-set! buf p (char->integer (car l)))
+	  (loop (cdr l) (add1 p))))
+
+      (updcrc buf len)
+      (set! bytes_in (+ bytes_in len)))
+
+    len))
+
+(define (put_byte c)
+  (string-set! outbuf outcnt (integer->char (bitwise-and #xFF c)))
+  (set! outcnt (add1 outcnt))
+  (when (= outcnt OUTBUFSIZ)
+    (flush_outbuf)))
+
+;; /* Output a 16 bit value, lsb first */
+(define (put_short w)
+  (if (< outcnt (- OUTBUFSIZ 2))
+      (begin
+	(string-set! outbuf outcnt (integer->char (bitwise-and #xFF w)))
+	(string-set! outbuf (add1 outcnt) (integer->char (bitwise-and #xFF (>> w 8))))
+	(set! outcnt (+ outcnt 2)))
+      (begin
+	(put_byte w)
+	(put_byte (>> w 8)))))
+
+;; /* Output a 32 bit value to the bit stream, lsb first */
+(define (put_long n)
+  (put_short n)
+  (put_short (>> n 16)))
+
+(define outcnt 0)
+(define bytes_out 0)
+(define outbuf (make-string OUTBUFSIZ))
+
+;; /* ===========================================================================
+;;  * Write the output buffer outbuf[0..outcnt-1] and update bytes_out.
+;;  * (used for the compressed data only)
+;;  */
+(define (flush_outbuf)
+  (unless (= outcnt 0)
+
+    (display (substring outbuf 0 outcnt) ofd)
+
+    (set! bytes_out (+ bytes_out outcnt))
+    (set! outcnt 0)))
+
+(define ifd #f)
+(define ofd #f)
+
+(define (zip in out origname time_stamp)
+
+    (define  flags (if origname #x8 0)) ;; /* general purpose bit flags */
+    (define time_stamp 0)
+
+    (set! ifd in)
+    (set! ofd out)
+    (set! outcnt 0)
+
+    ;; /* Write the header to the gzip file. See algorithm.doc for the format */
+    (put_byte #o037) ;; /* magic header */
+    (put_byte #o213)
+    (put_byte 8) ;; /* compression method */
+
+    (put_byte flags);; /* general flags */
+    (put_long time_stamp);
+
+    ;; /* Write deflated file to zip file */
+    (updcrc #f 0)
+
+    (bi_init)
+    (ct_init)
+
+    (put_byte (lm_init LEVEL));; /* extra flags */
+    (put_byte 3) ;; /* OS identifier */
+
+    (when origname
+      (for-each put_byte (map char->integer (string->list origname)))
+      (put_byte 0))
+
+    (deflate)
+
+    ;; /* Write the crc and uncompressed size */
+    (put_long (bitwise-xor crc #xffffffff))
+    (put_long bytes_in)
+
+    (flush_outbuf))
+
+(zip (open-input-file "OUTPUT") (open-output-file "x" 'replace)
+     "OUTPUT" (file-or-directory-modify-seconds "OUTPUT"))
+
+))))