diff options
Diffstat (limited to 'generic/tclHash.c')
| -rw-r--r-- | generic/tclHash.c | 33 |
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; } |