1/* 2 * hash_64 - 64 bit Fowler/Noll/Vo-0 FNV-1a hash code 3 * 4 * @(#) $Revision: 5.1 $ 5 * @(#) $Id: hash_64a.c,v 5.1 2009/06/30 09:01:38 chongo Exp $ 6 * @(#) $Source: /usr/local/src/cmd/fnv/RCS/hash_64a.c,v $ 7 * 8 *** 9 * 10 * Fowler/Noll/Vo hash 11 * 12 * The basis of this hash algorithm was taken from an idea sent 13 * as reviewer comments to the IEEE POSIX P1003.2 committee by: 14 * 15 * Phong Vo (http://www.research.att.com/info/kpv/) 16 * Glenn Fowler (http://www.research.att.com/~gsf/) 17 * 18 * In a subsequent ballot round: 19 * 20 * Landon Curt Noll (http://www.isthe.com/chongo/) 21 * 22 * improved on their algorithm. Some people tried this hash 23 * and found that it worked rather well. In an EMail message 24 * to Landon, they named it the ``Fowler/Noll/Vo'' or FNV hash. 25 * 26 * FNV hashes are designed to be fast while maintaining a low 27 * collision rate. The FNV speed allows one to quickly hash lots 28 * of data while maintaining a reasonable collision rate. See: 29 * 30 * http://www.isthe.com/chongo/tech/comp/fnv/index.html 31 * 32 * for more details as well as other forms of the FNV hash. 33 * 34 *** 35 * 36 * To use the recommended 64 bit FNV-1a hash, pass FNV1A_64_INIT as the 37 * Fnv64_t hashval argument to fnv_64a_buf() or fnv_64a_str(). 38 * 39 *** 40 * 41 * Please do not copyright this code. This code is in the public domain. 42 * 43 * LANDON CURT NOLL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, 44 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO 45 * EVENT SHALL LANDON CURT NOLL BE LIABLE FOR ANY SPECIAL, INDIRECT OR 46 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF 47 * USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR 48 * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR 49 * PERFORMANCE OF THIS SOFTWARE. 50 * 51 * By: 52 * chongo <Landon Curt Noll> /\oo/\ 53 * http://www.isthe.com/chongo/ 54 * 55 * Share and Enjoy! :-) 56 */ 57 58#include <stdlib.h> 59#include "fnv.h" 60 61 62/* 63 * FNV-1a defines the initial basis to be non-zero 64 */ 65#if !defined(HAVE_64BIT_LONG_LONG) 66const Fnv64_t fnv1a_64_init = { 0x84222325, 0xcbf29ce4 }; 67#endif /* ! HAVE_64BIT_LONG_LONG */ 68 69 70/* 71 * 64 bit magic FNV-1a prime 72 */ 73#if defined(HAVE_64BIT_LONG_LONG) 74#define FNV_64_PRIME ((Fnv64_t)0x100000001b3ULL) 75#else /* HAVE_64BIT_LONG_LONG */ 76#define FNV_64_PRIME_LOW ((unsigned long)0x1b3) /* lower bits of FNV prime */ 77#define FNV_64_PRIME_SHIFT (8) /* top FNV prime shift above 2^32 */ 78#endif /* HAVE_64BIT_LONG_LONG */ 79 80 81/* 82 * fnv_64a_str - perform a 64 bit Fowler/Noll/Vo FNV-1a hash on a buffer 83 * 84 * input: 85 * buf - start of buffer to hash 86 * hval - previous hash value or 0 if first call 87 * 88 * returns: 89 * 64 bit hash as a static hash type 90 * 91 * NOTE: To use the recommended 64 bit FNV-1a hash, use FNV1A_64_INIT as the 92 * hval arg on the first call to either fnv_64a_buf() or fnv_64a_str(). 93 */ 94uint64_t 95fnv_64a_str(char *str, uint64_t hval) 96{ 97 unsigned char *s = (unsigned char *)str; /* unsigned string */ 98 99#if defined(HAVE_64BIT_LONG_LONG) 100 101 /* 102 * FNV-1a hash each octet of the string 103 */ 104 while (*s) { 105 106 /* xor the bottom with the current octet */ 107 hval ^= (uint64_t)*s++; 108 109 /* multiply by the 64 bit FNV magic prime mod 2^64 */ 110#if defined(NO_FNV_GCC_OPTIMIZATION) 111 hval *= FNV_64_PRIME; 112#else /* NO_FNV_GCC_OPTIMIZATION */ 113 hval += (hval << 1) + (hval << 4) + (hval << 5) + 114 (hval << 7) + (hval << 8) + (hval << 40); 115#endif /* NO_FNV_GCC_OPTIMIZATION */ 116 } 117 118#else /* !HAVE_64BIT_LONG_LONG */ 119 120 unsigned long val[4]; /* hash value in base 2^16 */ 121 unsigned long tmp[4]; /* tmp 64 bit value */ 122 123 /* 124 * Convert Fnv64_t hval into a base 2^16 array 125 */ 126 val[0] = hval.w32[0]; 127 val[1] = (val[0] >> 16); 128 val[0] &= 0xffff; 129 val[2] = hval.w32[1]; 130 val[3] = (val[2] >> 16); 131 val[2] &= 0xffff; 132 133 /* 134 * FNV-1a hash each octet of the string 135 */ 136 while (*s) { 137 138 /* xor the bottom with the current octet */ 139 140 /* 141 * multiply by the 64 bit FNV magic prime mod 2^64 142 * 143 * Using 1099511628211, we have the following digits base 2^16: 144 * 145 * 0x0 0x100 0x0 0x1b3 146 * 147 * which is the same as: 148 * 149 * 0x0 1<<FNV_64_PRIME_SHIFT 0x0 FNV_64_PRIME_LOW 150 */ 151 /* multiply by the lowest order digit base 2^16 */ 152 tmp[0] = val[0] * FNV_64_PRIME_LOW; 153 tmp[1] = val[1] * FNV_64_PRIME_LOW; 154 tmp[2] = val[2] * FNV_64_PRIME_LOW; 155 tmp[3] = val[3] * FNV_64_PRIME_LOW; 156 /* multiply by the other non-zero digit */ 157 tmp[2] += val[0] << FNV_64_PRIME_SHIFT; /* tmp[2] += val[0] * 0x100 */ 158 tmp[3] += val[1] << FNV_64_PRIME_SHIFT; /* tmp[3] += val[1] * 0x100 */ 159 /* propagate carries */ 160 tmp[1] += (tmp[0] >> 16); 161 val[0] = tmp[0] & 0xffff; 162 tmp[2] += (tmp[1] >> 16); 163 val[1] = tmp[1] & 0xffff; 164 val[3] = tmp[3] + (tmp[2] >> 16); 165 val[2] = tmp[2] & 0xffff; 166 /* 167 * Doing a val[3] &= 0xffff; is not really needed since it simply 168 * removes multiples of 2^64. We can discard these excess bits 169 * outside of the loop when we convert to Fnv64_t. 170 */ 171 val[0] ^= (unsigned long)(*s++); 172 } 173 174 /* 175 * Convert base 2^16 array back into an Fnv64_t 176 */ 177 hval.w32[1] = ((val[3]<<16) | val[2]); 178 hval.w32[0] = ((val[1]<<16) | val[0]); 179 180#endif /* !HAVE_64BIT_LONG_LONG */ 181 182 /* return our new hash value */ 183 return hval; 184} 185