summaryrefslogtreecommitdiffstats
path: root/generic/tclObj.c
diff options
context:
space:
mode:
Diffstat (limited to 'generic/tclObj.c')
-rw-r--r--generic/tclObj.c35
1 files changed, 15 insertions, 20 deletions
diff --git a/generic/tclObj.c b/generic/tclObj.c
index 28d7a8a..6287b24 100644
--- a/generic/tclObj.c
+++ b/generic/tclObj.c
@@ -13,7 +13,7 @@
* See the file "license.terms" for information on usage and redistribution of
* this file, and for a DISCLAIMER OF ALL WARRANTIES.
*
- * RCS: @(#) $Id: tclObj.c,v 1.166 2009/12/29 16:54:44 dkf Exp $
+ * RCS: @(#) $Id: tclObj.c,v 1.167 2010/02/07 09:10:33 dkf Exp $
*/
#include "tclInt.h"
@@ -4037,30 +4037,25 @@ TclHashObjKey(
Tcl_HashTable *tablePtr, /* Hash table. */
void *keyPtr) /* Key from which to compute hash value. */
{
- Tcl_Obj *objPtr = (Tcl_Obj *) keyPtr;
- const char *string = TclGetString(objPtr);
- int length = objPtr->length;
- unsigned int result = 0;
- int i;
+ Tcl_Obj *objPtr = keyPtr;
+ register unsigned result = 0;
+ const unsigned char *string = (unsigned char *) TclGetString(objPtr);
+ const unsigned char *last = string + objPtr->length;
/*
- * 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 names used in practice. 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.
+ * Derived from Public Domain implementation by Landon Curt Noll at:
+ * http://www.isthe.com/chongo/src/fnv/hash_32.c
*/
- for (i=0 ; i<length ; i++) {
- result += (result << 3) + string[i];
+#define FNV_32_PRIME ((unsigned) 0x01000193)
+ while (string < last) {
+ result = (result * FNV_32_PRIME) ^ (*string++);
}
return result;
}