From: Chris Hanson <org/chris-hanson/cph>
Date: Fri, 16 Jun 1989 11:32:03 +0000 (+0000)
Subject: Change the string hashing algorithm one more time.  This one looks
X-Git-Tag: 20090517-FFI~12000
X-Git-Url: https://birchwood-abbey.net/git?a=commitdiff_plain;h=7df82a67da4e19915b49b8e5989ffe97cfa8ad01;p=mit-scheme.git

Change the string hashing algorithm one more time.  This one looks
like more of a winner than the previous one.
---

diff --git a/v7/src/microcode/intern.c b/v7/src/microcode/intern.c
index 32a034587..669e0a561 100644
--- a/v7/src/microcode/intern.c
+++ b/v7/src/microcode/intern.c
@@ -30,7 +30,7 @@ Technology nor of any adaptation thereof in any advertising,
 promotional, or sales literature without prior written consent from
 MIT in each case. */
 
-/* $Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/microcode/intern.c,v 9.47 1989/06/16 11:15:04 cph Exp $ */
+/* $Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/microcode/intern.c,v 9.48 1989/06/16 11:32:03 cph Exp $ */
 
 /* String hash functions and interning of symbols. */
 
@@ -41,19 +41,26 @@ MIT in each case. */
 
 /* Hashing strings */
 
-static long
+#define STRING_HASH_BITS 16
+
+static unsigned int
 string_hash (string)
      Pointer string;
 {
   fast unsigned char * scan;
   fast unsigned char * end;
-  fast long result;
+  fast unsigned int result;
 
   scan = ((unsigned char *) (string_pointer (string, 0)));
   end = (scan + (string_length (string)));
   result = 0;
   while (scan < end)
-    result = ((((result & 0x1fff) << 1) | (result >> 13)) ^ (*scan++));
+    {
+      result <<= 1;
+      result |= (result >> STRING_HASH_BITS);
+      result ^= (*scan++);
+      result &= ((1 << STRING_HASH_BITS) - 1);
+    }
   return (result);
 }