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-rw-r--r--generic/tclHash.c33
1 files changed, 13 insertions, 20 deletions
diff --git a/generic/tclHash.c b/generic/tclHash.c
index 9ed941e..f3c4b3a 100644
--- a/generic/tclHash.c
+++ b/generic/tclHash.c
@@ -10,7 +10,7 @@
* See the file "license.terms" for information on usage and redistribution of
* this file, and for a DISCLAIMER OF ALL WARRANTIES.
*
- * RCS: @(#) $Id: tclHash.c,v 1.39 2009/07/16 21:24:39 dgp Exp $
+ * RCS: @(#) $Id: tclHash.c,v 1.40 2010/02/07 09:10:33 dkf Exp $
*/
#include "tclInt.h"
@@ -866,36 +866,29 @@ CompareStringKeys(
*----------------------------------------------------------------------
*/
-static unsigned int
+static unsigned
HashStringKey(
Tcl_HashTable *tablePtr, /* Hash table. */
void *keyPtr) /* Key from which to compute hash value. */
{
register const char *string = (const char *) keyPtr;
- register unsigned int result;
+ register unsigned result = 0;
register int c;
/*
- * I tried a zillion different hash functions and asked many other people
- * for advice. Many people had their own favorite functions, all
- * different, but no-one had much idea why they were good ones. I chose
- * the one below (multiply by 9 and add new character) because of the
- * following reasons:
+ * This is the (32-bit) Fowler/Noll/Vo hash algorithm. This has the
+ * property of being a reasonably good non-cryptographic hash function for
+ * short string words, i.e., virtually all command and namespace names. It
+ * is also faster than Tcl's original algorithm on Intel x86, where there
+ * is a fast built-in multiply assembly instruction.
*
- * 1. Multiplying by 10 is perfect for keys that are decimal strings, and
- * multiplying by 9 is just about as good.
- * 2. Times-9 is (shift-left-3) plus (old). This means that each
- * character's bits hang around in the low-order bits of the hash value
- * for ever, plus they spread fairly rapidly up to the high-order bits
- * to fill out the hash value. This seems works well both for decimal
- * and non-decimal strings, but isn't strong against maliciously-chosen
- * keys.
+ * Derived from Public Domain implementation by Landon Curt Noll at:
+ * http://www.isthe.com/chongo/src/fnv/hash_32.c
*/
- result = 0;
-
- for (c=*string++ ; c ; c=*string++) {
- result += (result<<3) + c;
+#define FNV_32_PRIME ((unsigned) 0x01000193)
+ while ((c=*string++)) {
+ result = (result * FNV_32_PRIME) ^ c;
}
return result;
}