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Diffstat (limited to 'lib/fnv/hash_64a.c')
| -rw-r--r-- | lib/fnv/hash_64a.c | 291 |
1 files changed, 291 insertions, 0 deletions
diff --git a/lib/fnv/hash_64a.c b/lib/fnv/hash_64a.c new file mode 100644 index 0000000000..6660f92ddf --- /dev/null +++ b/lib/fnv/hash_64a.c @@ -0,0 +1,291 @@ +/* + * hash_64 - 64 bit Fowler/Noll/Vo-0 FNV-1a hash code + * + * @(#) $Revision: 5.1 $ + * @(#) $Id: hash_64a.c,v 5.1 2009/06/30 09:01:38 chongo Exp $ + * @(#) $Source: /usr/local/src/cmd/fnv/RCS/hash_64a.c,v $ + * + *** + * + * Fowler/Noll/Vo hash + * + * The basis of this hash algorithm was taken from an idea sent + * as reviewer comments to the IEEE POSIX P1003.2 committee by: + * + * Phong Vo (http://www.research.att.com/info/kpv/) + * Glenn Fowler (http://www.research.att.com/~gsf/) + * + * In a subsequent ballot round: + * + * Landon Curt Noll (http://www.isthe.com/chongo/) + * + * improved on their algorithm. Some people tried this hash + * and found that it worked rather well. In an EMail message + * to Landon, they named it the ``Fowler/Noll/Vo'' or FNV hash. + * + * FNV hashes are designed to be fast while maintaining a low + * collision rate. The FNV speed allows one to quickly hash lots + * of data while maintaining a reasonable collision rate. See: + * + * http://www.isthe.com/chongo/tech/comp/fnv/index.html + * + * for more details as well as other forms of the FNV hash. + * + *** + * + * To use the recommended 64 bit FNV-1a hash, pass FNV1A_64_INIT as the + * Fnv64_t hashval argument to fnv_64a_buf() or fnv_64a_str(). + * + *** + * + * Please do not copyright this code. This code is in the public domain. + * + * LANDON CURT NOLL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, + * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO + * EVENT SHALL LANDON CURT NOLL BE LIABLE FOR ANY SPECIAL, INDIRECT OR + * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF + * USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR + * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR + * PERFORMANCE OF THIS SOFTWARE. + * + * By: + * chongo <Landon Curt Noll> /\oo/\ + * http://www.isthe.com/chongo/ + * + * Share and Enjoy! :-) + */ + +#include <stdlib.h> +#include "fnv.h" + + +/* + * FNV-1a defines the initial basis to be non-zero + */ +#if !defined(HAVE_64BIT_LONG_LONG) +const Fnv64_t fnv1a_64_init = { 0x84222325, 0xcbf29ce4 }; +#endif /* ! HAVE_64BIT_LONG_LONG */ + + +/* + * 64 bit magic FNV-1a prime + */ +#if defined(HAVE_64BIT_LONG_LONG) +#define FNV_64_PRIME ((Fnv64_t)0x100000001b3ULL) +#else /* HAVE_64BIT_LONG_LONG */ +#define FNV_64_PRIME_LOW ((unsigned long)0x1b3) /* lower bits of FNV prime */ +#define FNV_64_PRIME_SHIFT (8) /* top FNV prime shift above 2^32 */ +#endif /* HAVE_64BIT_LONG_LONG */ + + +/* + * fnv_64a_buf - perform a 64 bit Fowler/Noll/Vo FNV-1a hash on a buffer + * + * input: + * buf - start of buffer to hash + * len - length of buffer in octets + * hval - previous hash value or 0 if first call + * + * returns: + * 64 bit hash as a static hash type + * + * NOTE: To use the recommended 64 bit FNV-1a hash, use FNV1A_64_INIT as the + * hval arg on the first call to either fnv_64a_buf() or fnv_64a_str(). + */ +Fnv64_t +fnv_64a_buf(void *buf, size_t len, Fnv64_t hval) +{ + unsigned char *bp = (unsigned char *)buf; /* start of buffer */ + unsigned char *be = bp + len; /* beyond end of buffer */ + +#if defined(HAVE_64BIT_LONG_LONG) + /* + * FNV-1a hash each octet of the buffer + */ + while (bp < be) { + + /* xor the bottom with the current octet */ + hval ^= (Fnv64_t)*bp++; + + /* multiply by the 64 bit FNV magic prime mod 2^64 */ +#if defined(NO_FNV_GCC_OPTIMIZATION) + hval *= FNV_64_PRIME; +#else /* NO_FNV_GCC_OPTIMIZATION */ + hval += (hval << 1) + (hval << 4) + (hval << 5) + + (hval << 7) + (hval << 8) + (hval << 40); +#endif /* NO_FNV_GCC_OPTIMIZATION */ + } + +#else /* HAVE_64BIT_LONG_LONG */ + + unsigned long val[4]; /* hash value in base 2^16 */ + unsigned long tmp[4]; /* tmp 64 bit value */ + + /* + * Convert Fnv64_t hval into a base 2^16 array + */ + val[0] = hval.w32[0]; + val[1] = (val[0] >> 16); + val[0] &= 0xffff; + val[2] = hval.w32[1]; + val[3] = (val[2] >> 16); + val[2] &= 0xffff; + + /* + * FNV-1a hash each octet of the buffer + */ + while (bp < be) { + + /* xor the bottom with the current octet */ + val[0] ^= (unsigned long)*bp++; + + /* + * multiply by the 64 bit FNV magic prime mod 2^64 + * + * Using 0x100000001b3 we have the following digits base 2^16: + * + * 0x0 0x100 0x0 0x1b3 + * + * which is the same as: + * + * 0x0 1<<FNV_64_PRIME_SHIFT 0x0 FNV_64_PRIME_LOW + */ + /* multiply by the lowest order digit base 2^16 */ + tmp[0] = val[0] * FNV_64_PRIME_LOW; + tmp[1] = val[1] * FNV_64_PRIME_LOW; + tmp[2] = val[2] * FNV_64_PRIME_LOW; + tmp[3] = val[3] * FNV_64_PRIME_LOW; + /* multiply by the other non-zero digit */ + tmp[2] += val[0] << FNV_64_PRIME_SHIFT; /* tmp[2] += val[0] * 0x100 */ + tmp[3] += val[1] << FNV_64_PRIME_SHIFT; /* tmp[3] += val[1] * 0x100 */ + /* propagate carries */ + tmp[1] += (tmp[0] >> 16); + val[0] = tmp[0] & 0xffff; + tmp[2] += (tmp[1] >> 16); + val[1] = tmp[1] & 0xffff; + val[3] = tmp[3] + (tmp[2] >> 16); + val[2] = tmp[2] & 0xffff; + /* + * Doing a val[3] &= 0xffff; is not really needed since it simply + * removes multiples of 2^64. We can discard these excess bits + * outside of the loop when we convert to Fnv64_t. + */ + } + + /* + * Convert base 2^16 array back into an Fnv64_t + */ + hval.w32[1] = ((val[3]<<16) | val[2]); + hval.w32[0] = ((val[1]<<16) | val[0]); + +#endif /* HAVE_64BIT_LONG_LONG */ + + /* return our new hash value */ + return hval; +} + + +/* + * fnv_64a_str - perform a 64 bit Fowler/Noll/Vo FNV-1a hash on a buffer + * + * input: + * buf - start of buffer to hash + * hval - previous hash value or 0 if first call + * + * returns: + * 64 bit hash as a static hash type + * + * NOTE: To use the recommended 64 bit FNV-1a hash, use FNV1A_64_INIT as the + * hval arg on the first call to either fnv_64a_buf() or fnv_64a_str(). + */ +Fnv64_t +fnv_64a_str(char *str, Fnv64_t hval) +{ + unsigned char *s = (unsigned char *)str; /* unsigned string */ + +#if defined(HAVE_64BIT_LONG_LONG) + + /* + * FNV-1a hash each octet of the string + */ + while (*s) { + + /* xor the bottom with the current octet */ + hval ^= (Fnv64_t)*s++; + + /* multiply by the 64 bit FNV magic prime mod 2^64 */ +#if defined(NO_FNV_GCC_OPTIMIZATION) + hval *= FNV_64_PRIME; +#else /* NO_FNV_GCC_OPTIMIZATION */ + hval += (hval << 1) + (hval << 4) + (hval << 5) + + (hval << 7) + (hval << 8) + (hval << 40); +#endif /* NO_FNV_GCC_OPTIMIZATION */ + } + +#else /* !HAVE_64BIT_LONG_LONG */ + + unsigned long val[4]; /* hash value in base 2^16 */ + unsigned long tmp[4]; /* tmp 64 bit value */ + + /* + * Convert Fnv64_t hval into a base 2^16 array + */ + val[0] = hval.w32[0]; + val[1] = (val[0] >> 16); + val[0] &= 0xffff; + val[2] = hval.w32[1]; + val[3] = (val[2] >> 16); + val[2] &= 0xffff; + + /* + * FNV-1a hash each octet of the string + */ + while (*s) { + + /* xor the bottom with the current octet */ + + /* + * multiply by the 64 bit FNV magic prime mod 2^64 + * + * Using 1099511628211, we have the following digits base 2^16: + * + * 0x0 0x100 0x0 0x1b3 + * + * which is the same as: + * + * 0x0 1<<FNV_64_PRIME_SHIFT 0x0 FNV_64_PRIME_LOW + */ + /* multiply by the lowest order digit base 2^16 */ + tmp[0] = val[0] * FNV_64_PRIME_LOW; + tmp[1] = val[1] * FNV_64_PRIME_LOW; + tmp[2] = val[2] * FNV_64_PRIME_LOW; + tmp[3] = val[3] * FNV_64_PRIME_LOW; + /* multiply by the other non-zero digit */ + tmp[2] += val[0] << FNV_64_PRIME_SHIFT; /* tmp[2] += val[0] * 0x100 */ + tmp[3] += val[1] << FNV_64_PRIME_SHIFT; /* tmp[3] += val[1] * 0x100 */ + /* propagate carries */ + tmp[1] += (tmp[0] >> 16); + val[0] = tmp[0] & 0xffff; + tmp[2] += (tmp[1] >> 16); + val[1] = tmp[1] & 0xffff; + val[3] = tmp[3] + (tmp[2] >> 16); + val[2] = tmp[2] & 0xffff; + /* + * Doing a val[3] &= 0xffff; is not really needed since it simply + * removes multiples of 2^64. We can discard these excess bits + * outside of the loop when we convert to Fnv64_t. + */ + val[0] ^= (unsigned long)(*s++); + } + + /* + * Convert base 2^16 array back into an Fnv64_t + */ + hval.w32[1] = ((val[3]<<16) | val[2]); + hval.w32[0] = ((val[1]<<16) | val[0]); + +#endif /* !HAVE_64BIT_LONG_LONG */ + + /* return our new hash value */ + return hval; +} |