apache版time33
unsigned long time33(char const *str, int *len) { unsigned long hash = 0; const char *p=str; if (*len<=0) { for(p = str; *p; p++) { hash = hash * 33 + *p; } *len = p - str; } else { int i = *len; for (p = str;i; i--, p++) { hash = hash * 33 + *p; } } return hash; }
简单版time33
uint32_t time33(char const *str, int len) { unsigned long hash = 0; for (int i = 0; i < len; i++) { hash = hash *33 + (unsigned long) str[i]; } return hash; } nginx使用的是time31,Tokyo Cabinet使用time37,Java里使用的是Time32
Bob在他的文章说，小写英文词汇适合33, 大小写混合使用65。time33比较适合的是英文词汇的hash.
Bobhash算法
#include/* defines uint32_t etc */ #include /* attempt to define endianness */ #ifdef linux # include /* attempt to define endianness */ #endif/* * My best guess at if you are big-endian or little-endian. This may * need adjustment. */ #if (defined(__BYTE_ORDER) && defined(__LITTLE_ENDIAN) && \ __BYTE_ORDER == __LITTLE_ENDIAN) || \ (defined(i386) || defined(__i386__) || defined(__i486__) || \ defined(__i586__) || defined(__i686__) || defined(vax) || defined(MIPSEL)) # define HASH_LITTLE_ENDIAN 1 # define HASH_BIG_ENDIAN 0 #elif (defined(__BYTE_ORDER) && defined(__BIG_ENDIAN) && \ __BYTE_ORDER == __BIG_ENDIAN) || \ (defined(sparc) || defined(POWERPC) || defined(mc68000) || defined(sel)) # define HASH_LITTLE_ENDIAN 0 # define HASH_BIG_ENDIAN 1 #else # define HASH_LITTLE_ENDIAN 0 # define HASH_BIG_ENDIAN 0 #endif #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 -= 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; \ }#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); \ }uint32_t bob_hash( const void *key, size_t length, uint32_t initval) { uint32_t a,b,c; /* internal state */ union { const void *ptr; size_t i; } u; /* needed for Mac Powerbook G4 */ /* Set up the internal state */ a = b = c = 0xdeadbeef + ((uint32_t)length) + initval; u.ptr = key; if (HASH_LITTLE_ENDIAN && ((u.i & 0x3) == 0)) { const uint32_t *k = (const uint32_t *)key; /* read 32-bit chunks */ const uint8_t *k8; /*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */ while (length > 12) { a += k[0]; b += k[1]; c += k[2]; mix(a,b,c); length -= 12; k += 3; } /*----------------------------- handle the last (probably partial) block */ /* * "k[2]&0xffffff" actually reads beyond the end of the string, but * then masks off the part it's not allowed to read. Because the * string is aligned, the masked-off tail is in the same word as the * rest of the string. Every machine with memory protection I've seen * does it on word boundaries, so is OK with this. But VALGRIND will * still catch it and complain. The masking trick does make the hash * noticably faster for short strings (like English words). */ #ifndef VALGRIND switch(length) { case 12: c+=k[2]; b+=k[1]; a+=k[0]; break; case 11: c+=k[2]&0xffffff; b+=k[1]; a+=k[0]; break; case 10: c+=k[2]&0xffff; b+=k[1]; a+=k[0]; break; case 9 : c+=k[2]&0xff; b+=k[1]; a+=k[0]; break; case 8 : b+=k[1]; a+=k[0]; break; case 7 : b+=k[1]&0xffffff; a+=k[0]; break; case 6 : b+=k[1]&0xffff; a+=k[0]; break; case 5 : b+=k[1]&0xff; a+=k[0]; break; case 4 : a+=k[0]; break; case 3 : a+=k[0]&0xffffff; break; case 2 : a+=k[0]&0xffff; break; case 1 : a+=k[0]&0xff; break; case 0 : return c; /* zero length strings require no mixing */ }#else /* make valgrind happy */ k8 = (const uint8_t *)k; switch(length) { case 12: c+=k[2]; b+=k[1]; a+=k[0]; break; case 11: c+=((uint32_t)k8[10])<<16; /* fall through */ case 10: c+=((uint32_t)k8[9])<<8; /* fall through */ case 9 : c+=k8[8]; /* fall through */ case 8 : b+=k[1]; a+=k[0]; break; case 7 : b+=((uint32_t)k8[6])<<16; /* fall through */ case 6 : b+=((uint32_t)k8[5])<<8; /* fall through */ case 5 : b+=k8[4]; /* fall through */ case 4 : a+=k[0]; break; case 3 : a+=((uint32_t)k8[2])<<16; /* fall through */ case 2 : a+=((uint32_t)k8[1])<<8; /* fall through */ case 1 : a+=k8[0]; break; case 0 : return c; }#endif /* !valgrind */ } else if (HASH_LITTLE_ENDIAN && ((u.i & 0x1) == 0)) { const uint16_t *k = (const uint16_t *)key; /* read 16-bit chunks */ const uint8_t *k8; /*--------------- all but last block: aligned reads and different mixing */ while (length > 12) { a += k[0] + (((uint32_t)k[1])<<16); b += k[2] + (((uint32_t)k[3])<<16); c += k[4] + (((uint32_t)k[5])<<16); mix(a,b,c); length -= 12; k += 6; } /*----------------------------- handle the last (probably partial) block */ k8 = (const uint8_t *)k; switch(length) { case 12: c+=k[4]+(((uint32_t)k[5])<<16); b+=k[2]+(((uint32_t)k[3])<<16); a+=k[0]+(((uint32_t)k[1])<<16); break; case 11: c+=((uint32_t)k8[10])<<16; /* fall through */ case 10: c+=k[4]; b+=k[2]+(((uint32_t)k[3])<<16); a+=k[0]+(((uint32_t)k[1])<<16); break; case 9 : c+=k8[8]; /* fall through */ case 8 : b+=k[2]+(((uint32_t)k[3])<<16); a+=k[0]+(((uint32_t)k[1])<<16); break; case 7 : b+=((uint32_t)k8[6])<<16; /* fall through */ case 6 : b+=k[2]; a+=k[0]+(((uint32_t)k[1])<<16); break; case 5 : b+=k8[4]; /* fall through */ case 4 : a+=k[0]+(((uint32_t)k[1])<<16); break; case 3 : a+=((uint32_t)k8[2])<<16; /* fall through */ case 2 : a+=k[0]; break; case 1 : a+=k8[0]; break; case 0 : return c; /* zero length requires no mixing */ } } else { /* need to read the key one byte at a time */ const uint8_t *k = (const uint8_t *)key; /*--------------- all but the last block: affect some 32 bits of (a,b,c) */ while (length > 12) { a += k[0]; a += ((uint32_t)k[1])<<8; a += ((uint32_t)k[2])<<16; a += ((uint32_t)k[3])<<24; b += k[4]; b += ((uint32_t)k[5])<<8; b += ((uint32_t)k[6])<<16; b += ((uint32_t)k[7])<<24; c += k[8]; c += ((uint32_t)k[9])<<8; c += ((uint32_t)k[10])<<16; c += ((uint32_t)k[11])<<24; mix(a,b,c); length -= 12; k += 12; } /*-------------------------------- last block: affect all 32 bits of (c) */ switch(length) /* all the case statements fall through */ { case 12: c+=((uint32_t)k[11])<<24; case 11: c+=((uint32_t)k[10])<<16; case 10: c+=((uint32_t)k[9])<<8; case 9 : c+=k[8]; case 8 : b+=((uint32_t)k[7])<<24; case 7 : b+=((uint32_t)k[6])<<16; case 6 : b+=((uint32_t)k[5])<<8; case 5 : b+=k[4]; case 4 : a+=((uint32_t)k[3])<<24; case 3 : a+=((uint32_t)k[2])<<16; case 2 : a+=((uint32_t)k[1])<<8; case 1 : a+=k[0]; break; case 0 : return c; } } final(a,b,c); return c; }
bob is about 2 cycles/byte, works well on 32-bit platforms, and can produce a 32 or 64 bit hash. SpookyHash (2011) is specific to 64-bit platforms, is about 1/3 cycle per byte, and produces a 32, 64, or 128 bit hash.