diff options
Diffstat (limited to 'generic/tclObj.c')
| -rw-r--r-- | generic/tclObj.c | 35 |
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; } |