git.m6w6.name Git - m6w6/libmemcached/blob - libhashkit/hsieh.cc

   1 /*  vim:expandtab:shiftwidth=2:tabstop=2:smarttab:
   2  *
   3  *  HashKit library
   4  *
   5  *  Copyright (C) 2011-2012 Data Differential, http://datadifferential.com/
   6  *  Copyright (C) 2006-2009 Brian Aker All rights reserved.
   7  *
   8  *  Redistribution and use in source and binary forms, with or without
   9  *  modification, are permitted provided that the following conditions are
  10  *  met:
  11  *
  12  *      * Redistributions of source code must retain the above copyright
  13  *  notice, this list of conditions and the following disclaimer.
  14  *
  15  *      * Redistributions in binary form must reproduce the above
  16  *  copyright notice, this list of conditions and the following disclaimer
  17  *  in the documentation and/or other materials provided with the
  18  *  distribution.
  19  *
  20  *      * The names of its contributors may not be used to endorse or
  21  *  promote products derived from this software without specific prior
  22  *  written permission.
  23  *
  24  *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  25  *  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  26  *  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  27  *  A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  28  *  OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  29  *  SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  30  *  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  31  *  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  32  *  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  33  *  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  34  *  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  35  *
  36  */
  37
  38 /* By Paul Hsieh (C) 2004, 2005.  Covered under the Paul Hsieh
  39  * derivative license.
  40  * See: http://www.azillionmonkeys.com/qed/weblicense.html for license
  41  * details.
  42  * http://www.azillionmonkeys.com/qed/hash.html
  43 */
  44
  45 #include <libhashkit/common.h>
  46
  47 #undef get16bits
  48 #if (defined(__GNUC__) && defined(__i386__))
  49 #define get16bits(d) (*((const uint16_t *) (d)))
  50 #endif
  51
  52 #if !defined (get16bits)
  53 #define get16bits(d) ((((uint32_t)(((const uint8_t *)(d))[1])) << 8)\
  54                       +(uint32_t)(((const uint8_t *)(d))[0]) )
  55 #endif
  56
  57 #ifdef HAVE_HSIEH_HASH
  58 uint32_t hashkit_hsieh(const char *key, size_t key_length, void *)
  59 {
  60   uint32_t hash = 0, tmp;
  61   int rem;
  62
  63   if (key_length <= 0 || key == NULL)
  64     return 0;
  65
  66   rem = key_length & 3;
  67   key_length >>= 2;
  68
  69   /* Main loop */
  70   for (;key_length > 0; key_length--)
  71   {
  72     hash  += get16bits (key);
  73     tmp    = (get16bits (key+2) << 11) ^ hash;
  74     hash   = (hash << 16) ^ tmp;
  75     key  += 2*sizeof (uint16_t);
  76     hash  += hash >> 11;
  77   }
  78
  79   /* Handle end cases */
  80   switch (rem)
  81   {
  82   case 3: hash += get16bits (key);
  83           hash ^= hash << 16;
  84           hash ^= (uint32_t)key[sizeof (uint16_t)] << 18;
  85           hash += hash >> 11;
  86           break;
  87   case 2: hash += get16bits (key);
  88           hash ^= hash << 11;
  89           hash += hash >> 17;
  90           break;
  91   case 1: hash += (unsigned char)(*key);
  92           hash ^= hash << 10;
  93           hash += hash >> 1;
  94   default:
  95           break;
  96   }
  97
  98   /* Force "avalanching" of final 127 bits */
  99   hash ^= hash << 3;
 100   hash += hash >> 5;
 101   hash ^= hash << 4;
 102   hash += hash >> 17;
 103   hash ^= hash << 25;
 104   hash += hash >> 6;
 105
 106   return hash;
 107 }
 108 #else
 109 uint32_t hashkit_hsieh(const char *, size_t , void *)
 110 {
 111   return 0;
 112 }
 113 #endif