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optimize null and one-argument lists

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svn: r18736
This commit is contained in:
Eli Barzilay 2010-04-06 15:26:15 +00:00
parent cc3c334026
commit 90acb35315
1 changed files with 42 additions and 36 deletions
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78
collects/scheme/list.ss
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@ -193,42 +193,48 @@
;; shorter ones too, but that adds a ton of code to the result (about 2k).
(define-syntax-rule (no-key x) x)
(unless (list? l) (raise-type-error 'remove-duplicates "list" l))
(let ([h (cond [(< (length l) 40) #f]
[(eq? =? eq?) (make-hasheq)]
[(eq? =? equal?) (make-hash)]
[else #f])])
(if h
;; Using a hash table when the list is long enough and when using
;; `equal?' or `eq?'. The length threshold (40) was determined by
;; trying it out with lists of length n holding (random n) numbers.
(let-syntax ([loop
(syntax-rules ()
[(_ getkey)
(let loop ([l l])
(if (null? l)
l
(let* ([x (car l)] [k (getkey x)] [l (cdr l)])
(if (hash-ref h k #f)
(loop l)
(begin (hash-set! h k #t)
(cons x (loop l)))))))])])
(if key (loop key) (loop no-key)))
;; plain n^2 list traversal (optimized for common cases)
(let ([key (or key (lambda (x) x))])
(let-syntax ([loop (syntax-rules ()
[(_ search)
(let loop ([l l] [seen null])
(if (null? l)
l
(let* ([x (car l)] [k (key x)] [l (cdr l)])
(if (search k seen)
(loop l seen)
(cons x (loop l (cons k seen)))))))])])
(cond [(eq? =? equal?) (loop member)]
[(eq? =? eq?) (loop memq)]
[(eq? =? eqv?) (loop memv)]
[else (loop (lambda (x seen)
(ormap (lambda (y) (=? x y)) seen)))]))))))
(let* ([len (length l)]
[h (cond [(<= len 1) #t]
[(<= len 40) #f]
[(eq? =? eq?) (make-hasheq)]
[(eq? =? equal?) (make-hash)]
[else #f])])
(case h
[(#t) l]
[(#f)
;; plain n^2 list traversal (optimized for common cases) for short lists
;; and for equalities other than `eq?' or `equal?' The length threshold
;; above (40) was determined by trying it out with lists of length n
;; holding (random n) numbers.
(let ([key (or key (lambda (x) x))])
(let-syntax ([loop (syntax-rules ()
[(_ search)
(let loop ([l l] [seen null])
(if (null? l)
l
(let* ([x (car l)] [k (key x)] [l (cdr l)])
(if (search k seen)
(loop l seen)
(cons x (loop l (cons k seen)))))))])])
(cond [(eq? =? equal?) (loop member)]
[(eq? =? eq?) (loop memq)]
[(eq? =? eqv?) (loop memv)]
[else (loop (lambda (x seen)
(ormap (lambda (y) (=? x y)) seen)))])))]
[else
;; Use a hash for long lists with simple hash tables.
(let-syntax ([loop
(syntax-rules ()
[(_ getkey)
(let loop ([l l])
(if (null? l)
l
(let* ([x (car l)] [k (getkey x)] [l (cdr l)])
(if (hash-ref h k #f)
(loop l)
(begin (hash-set! h k #t)
(cons x (loop l)))))))])])
(if key (loop key) (loop no-key)))])))
(define (filter-map f l . ls)
(unless (and (procedure? f) (procedure-arity-includes? f (add1 (length ls))))