From 1b79030aacf372368022de9fdb05a1896ca659b3 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Sat, 31 Jan 2009 03:04:09 +0000
Subject: [PATCH] improve 'equal' hashing on lists

svn: r13332
---
 src/mzscheme/src/hash.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/mzscheme/src/hash.c b/src/mzscheme/src/hash.c
index e3c631d453..e37fd7c0de 100644
--- a/src/mzscheme/src/hash.c
+++ b/src/mzscheme/src/hash.c
@@ -1022,7 +1022,11 @@ static long equal_hash_key(Scheme_Object *o, long k, Hash_Info *hi)
     {
 #     include "mzhashchk.inc"
       hi->depth += 2;
+      k = (k << 3) + k;
       k += equal_hash_key(SCHEME_CAR(o), 0, hi);
+      /* If it's a list, don't count cdr direction as depth: */
+      if (scheme_is_list(o))
+        hi->depth -= 2;
       o = SCHEME_CDR(o);
       break;
     }
@@ -1030,6 +1034,7 @@ static long equal_hash_key(Scheme_Object *o, long k, Hash_Info *hi)
     {
 #     include "mzhashchk.inc"
       hi->depth += 2;
+      k = (k << 3) + k;
       k += equal_hash_key(SCHEME_CAR(o), 0, hi);
       o = SCHEME_CDR(o);
       break;