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/*-
* Public Domain 2014-2016 MongoDB, Inc.
* Public Domain 2008-2014 WiredTiger, Inc.
*
* This is free and unencumbered software released into the public domain.
*
* Anyone is free to copy, modify, publish, use, compile, sell, or
* distribute this software, either in source code form or as a compiled
* binary, for any purpose, commercial or non-commercial, and by any
* means.
*
* In jurisdictions that recognize copyright laws, the author or authors
* of this software dedicate any and all copyright interest in the
* software to the public domain. We make this dedication for the benefit
* of the public at large and to the detriment of our heirs and
* successors. We intend this dedication to be an overt act of
* relinquishment in perpetuity of all present and future rights to this
* software under copyright law.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
* IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
* OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
* OTHER DEALINGS IN THE SOFTWARE.
*/
/*
* 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
* uint64_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 "wt_internal.h"
/*
* This file contains a 64 bit hash implementation of the FNV 1a 64 bit hash
* function. The implementation is from a third party.
*
* The code has been updated to remove unnecessary content and better comply
* with WiredTiger coding standards. The original source code can be found at:
* FNV 1a 64 bit: http://www.isthe.com/chongo/src/fnv/hash_64a.c
*/
/*
* 64 bit FNV-1 non-zero initial basis
*
* The FNV-1 initial basis is the FNV-0 hash of the following 32 octets:
*
* chongo <Landon Curt Noll> /\../\
*
* NOTE: The \'s above are not back-slashing escape characters.
* They are literal ASCII backslash 0x5c characters.
*
* NOTE: The FNV-1a initial basis is the same value as FNV-1 by definition.
*/
#define FNV1A_64_INIT ((uint64_t)0xcbf29ce484222325ULL)
/*
* 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().
*/
static inline uint64_t
fnv_64a_buf(const void *buf, size_t len, uint64_t hval)
{
const unsigned char *bp = buf; /* start of buffer */
const unsigned char *be = bp + len; /* beyond end of buffer */
/*
* FNV-1a hash each octet of the buffer
*/
while (bp < be) {
/* xor the bottom with the current octet */
hval ^= (uint64_t)*bp++;
/*
* Multiply by the 64 bit FNV magic prime mod 2^64. The
* following shift operation is generally faster than
* a multiply operation.
*/
hval += (hval << 1) + (hval << 4) + (hval << 5) +
(hval << 7) + (hval << 8) + (hval << 40);
}
/* return our new hash value */
return (hval);
}
/*
* __wt_hash_fnv64 --
* WiredTiger wrapper around third party hash implementation.
*/
uint64_t
__wt_hash_fnv64(const void *string, size_t len)
{
return (fnv_64a_buf(string, len, FNV1A_64_INIT));
}
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