Module: ngircd.git Branch: master Commit: 1765f0ae0b8932a4977c181c07d174f124143cef URL: http://ngircd.barton.de/cgi-bin/gitweb.cgi?p=ngircd.git&a=commit;h=1765f0ae0... Author: Florian Westphal <fw@strlen.de> Date: Mon Jun 27 00:16:37 2011 +0200 hash: use more recent lookup3 algorithm instead of lookup2 Bob Jenkins published a newer hash function in May 2006, it has better distribution. See http://burtleburtle.net/bob/hash/doobs.html for lengthy comparisions. --- src/ngircd/hash.c | 82 ++++++++++++++++++++++++++++------------------------ 1 files changed, 44 insertions(+), 38 deletions(-) diff --git a/src/ngircd/hash.c b/src/ngircd/hash.c index 113133d..7b7976c 100644 --- a/src/ngircd/hash.c +++ b/src/ngircd/hash.c @@ -26,8 +26,7 @@ #include "exp.h" #include "hash.h" -static UINT32 jenkins_hash PARAMS((register UINT8 *k, register UINT32 length, - register UINT32 initval)); +static UINT32 jenkins_hash PARAMS((UINT8 *k, UINT32 length, UINT32 initval)); /** * Calculate hash value for a given string. @@ -46,66 +45,74 @@ Hash( const char *String ) } /* Hash */ /* - * This hash function originates from lookup2.c of Bob Jenkins - * (URL: <http://burtleburtle.net/bob/c/lookup2.c>): + * This hash function originates from lookup3.c of Bob Jenkins + * (URL: <http://burtleburtle.net/bob/c/lookup3.c>): * -------------------------------------------------------------------- - * lookup2.c, by Bob Jenkins, December 1996, Public Domain. - * hash(), hash2(), hash3, and mix() are externally useful functions. - * Routines to test the hash are included if SELF_TEST is defined. - * You can use this free for any purpose. It has no warranty. + * lookup3.c, by Bob Jenkins, May 2006, Public Domain. + * These are functions for producing 32-bit hashes for hash table lookup. + * hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final() + * are externally useful functions. Routines to test the hash are included + * if SELF_TEST is defined. You can use this free for any purpose. It's in + * the public domain. It has no warranty. * -------------------------------------------------------------------- * Not all of his functions are used here. */ -#define hashsize(n) ((UINT32)1<<(n)) +#define hashsize(n) ((uint32_t)1<<(n)) #define hashmask(n) (hashsize(n)-1) +#define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k)))) #define mix(a,b,c) \ { \ - a -= b; a -= c; a ^= (c>>13); \ - b -= c; b -= a; b ^= (a<<8); \ - c -= a; c -= b; c ^= (b>>13); \ - a -= b; a -= c; a ^= (c>>12); \ - b -= c; b -= a; b ^= (a<<16); \ - c -= a; c -= b; c ^= (b>>5); \ - a -= b; a -= c; a ^= (c>>3); \ - b -= c; b -= a; b ^= (a<<10); \ - c -= a; c -= b; c ^= (b>>15); \ + a -= c; a ^= rot(c, 4); c += b; \ + b -= a; b ^= rot(a, 6); a += c; \ + c -= b; c ^= rot(b, 8); b += a; \ + a -= c; a ^= rot(c,16); c += b; \ + b -= a; b ^= rot(a,19); a += c; \ + c -= b; c ^= rot(b, 4); b += a; \ } /* mix */ +#define final(a,b,c) \ +{ \ + c ^= b; c -= rot(b,14); \ + a ^= c; a -= rot(c,11); \ + b ^= a; b -= rot(a,25); \ + c ^= b; c -= rot(b,16); \ + a ^= c; a -= rot(c,4); \ + b ^= a; b -= rot(a,14); \ + c ^= b; c -= rot(b,24); \ +} + static UINT32 -jenkins_hash( register UINT8 *k, register UINT32 length, register UINT32 initval ) +jenkins_hash(UINT8 *k, UINT32 length, UINT32 initval) { /* k: the key * length: length of the key * initval: the previous hash, or an arbitrary value */ - - register UINT32 a,b,c,len; + UINT32 a,b,c; /* Set up the internal state */ - len = length; - a = b = 0x9e3779b9; /* the golden ratio; an arbitrary value */ - c = initval; /* the previous hash value */ + a = b = c = 0xdeadbeef + length + initval; /* handle most of the key */ - while (len >= 12) - { + while (length > 12) { a += (k[0] +((UINT32)k[1]<<8) +((UINT32)k[2]<<16) +((UINT32)k[3]<<24)); b += (k[4] +((UINT32)k[5]<<8) +((UINT32)k[6]<<16) +((UINT32)k[7]<<24)); c += (k[8] +((UINT32)k[9]<<8) +((UINT32)k[10]<<16)+((UINT32)k[11]<<24)); mix(a,b,c); - k += 12; len -= 12; + length -= 12; + k += 12; } - /* handle the last 11 bytes */ - c += length; - switch( (int)len ) /* all the case statements fall through */ + /*-------------------------------- last block: affect all 32 bits of (c) */ + switch(length) /* all the case statements fall through */ + { - case 11: c+=((UINT32)k[10]<<24); - case 10: c+=((UINT32)k[9]<<16); - case 9 : c+=((UINT32)k[8]<<8); - /* the first byte of c is reserved for the length */ + case 12: c+=((UINT32)k[11])<<24; + case 11: c+=((UINT32)k[10]<<16); + case 10: c+=((UINT32)k[9]<<8); + case 9 : c+=k[8]; case 8 : b+=((UINT32)k[7]<<24); case 7 : b+=((UINT32)k[6]<<16); case 6 : b+=((UINT32)k[5]<<8); @@ -114,11 +121,10 @@ jenkins_hash( register UINT8 *k, register UINT32 length, register UINT32 initval case 3 : a+=((UINT32)k[2]<<16); case 2 : a+=((UINT32)k[1]<<8); case 1 : a+=k[0]; - /* case 0: nothing left to add */ + break; + case 0 : return c; } - mix(a,b,c); - - /* report the result */ + final(a,b,c); return c; } /* jenkins_hash */