git.m6w6.name Git - m6w6/libmemcached/blob - libmemcached/memcached_hash.c

   1 #include "common.h"
   2
   3
   4 /* Defines */
   5 static uint64_t FNV_64_INIT= 0xcbf29ce484222325LL;
   6 static uint64_t FNV_64_PRIME= 0x100000001b3LL;
   7
   8 static uint32_t FNV_32_INIT= 2166136261UL;
   9 static uint32_t FNV_32_PRIME= 16777619;
  10
  11 /* Prototypes */
  12 static uint32_t internal_generate_hash(const char *key, size_t key_length);
  13 static uint32_t internal_generate_md5(const char *key, size_t key_length);
  14
  15 uint32_t memcached_generate_hash_value(const char *key, size_t key_length, memcached_hash hash_algorithm)
  16 {
  17   uint32_t hash= 1; /* Just here to remove compile warning */
  18   uint32_t x= 0;
  19
  20   switch (hash_algorithm)
  21   {
  22   case MEMCACHED_HASH_DEFAULT:
  23     hash= internal_generate_hash(key, key_length);
  24     break;
  25   case MEMCACHED_HASH_MD5:
  26     hash= internal_generate_md5(key, key_length);
  27     break;
  28   case MEMCACHED_HASH_CRC:
  29     hash= ((hash_crc32(key, key_length) >> 16) & 0x7fff);
  30     if (hash == 0)
  31       hash= 1;
  32     break;
  33     /* FNV hash'es lifted from Dustin Sallings work */
  34   case MEMCACHED_HASH_FNV1_64:
  35     {
  36       /* Thanks to pierre@demartines.com for the pointer */
  37       uint64_t temp_hash;
  38
  39       temp_hash= FNV_64_INIT;
  40       for (x= 0; x < key_length; x++)
  41       {
  42         temp_hash *= FNV_64_PRIME;
  43         temp_hash ^= key[x];
  44       }
  45       hash= (uint32_t)temp_hash;
  46     }
  47     break;
  48   case MEMCACHED_HASH_FNV1A_64:
  49     {
  50       hash= FNV_64_INIT;
  51       for (x= 0; x < key_length; x++)
  52       {
  53         hash ^= key[x];
  54         hash *= FNV_64_PRIME;
  55       }
  56     }
  57     break;
  58   case MEMCACHED_HASH_FNV1_32:
  59     {
  60       hash= FNV_32_INIT;
  61       for (x= 0; x < key_length; x++)
  62       {
  63         hash *= FNV_32_PRIME;
  64         hash ^= key[x];
  65       }
  66     }
  67     break;
  68   case MEMCACHED_HASH_FNV1A_32:
  69     {
  70       hash= FNV_32_INIT;
  71       for (x= 0; x < key_length; x++)
  72       {
  73         hash ^= key[x];
  74         hash *= FNV_32_PRIME;
  75       }
  76     }
  77     break;
  78     case MEMCACHED_HASH_HSIEH:
  79     {
  80 #ifdef HAVE_HSIEH_HASH
  81       hash= hsieh_hash(key, key_length);
  82 #endif
  83       break;
  84     }
  85     case MEMCACHED_HASH_MURMUR:
  86     {
  87       hash= murmur_hash(key, key_length);
  88       break;
  89     }
  90     case MEMCACHED_HASH_JENKINS:
  91     {
  92       hash=jenkins_hash(key, key_length, 13);
  93       break;
  94     }
  95     default:
  96     {
  97       WATCHPOINT_ASSERT(hash_algorithm);
  98       break;
  99     }
 100   }
 101   return hash;
 102 }
 103
 104 uint32_t generate_hash(memcached_st *ptr, const char *key, size_t key_length)
 105 {
 106   uint32_t hash= 1; /* Just here to remove compile warning */
 107
 108
 109   WATCHPOINT_ASSERT(ptr->number_of_hosts);
 110
 111   if (ptr->number_of_hosts == 1)
 112     return 0;
 113
 114   hash= memcached_generate_hash_value(key, key_length, ptr->hash);
 115   WATCHPOINT_ASSERT(hash);
 116   return hash;
 117 }
 118
 119 static uint32_t dispatch_host(memcached_st *ptr, uint32_t hash)
 120 {
 121   switch (ptr->distribution)
 122   {
 123   case MEMCACHED_DISTRIBUTION_CONSISTENT:
 124   case MEMCACHED_DISTRIBUTION_CONSISTENT_KETAMA:
 125     {
 126       uint32_t num= ptr->continuum_points_counter;
 127       WATCHPOINT_ASSERT(ptr->continuum);
 128
 129       hash= hash;
 130       memcached_continuum_item_st *begin, *end, *left, *right, *middle;
 131       begin= left= ptr->continuum;
 132       end= right= ptr->continuum + num;
 133
 134       while (left < right)
 135       {
 136         middle= left + (right - left) / 2;
 137         if (middle->value < hash)
 138           left= middle + 1;
 139         else
 140           right= middle;
 141       }
 142       if (right == end)
 143         right= begin;
 144       return right->index;
 145     }
 146     break;
 147   case MEMCACHED_DISTRIBUTION_MODULA:
 148     return hash % ptr->number_of_hosts;
 149   case MEMCACHED_DISTRIBUTION_RANDOM:
 150     return random() % ptr->number_of_hosts;
 151   default:
 152     WATCHPOINT_ASSERT(0); /* We have added a distribution without extending the logic */
 153     return hash % ptr->number_of_hosts;
 154   }
 155
 156   /* NOTREACHED */
 157 }
 158
 159 /*
 160   One day make this public, and have it return the actual memcached_server_st
 161   to the calling application.
 162 */
 163 uint32_t memcached_generate_hash(memcached_st *ptr, const char *key, size_t key_length)
 164 {
 165   uint32_t hash= 1; /* Just here to remove compile warning */
 166
 167   WATCHPOINT_ASSERT(ptr->number_of_hosts);
 168
 169   if (ptr->number_of_hosts == 1)
 170     return 0;
 171
 172   if (ptr->flags & MEM_HASH_WITH_PREFIX_KEY)
 173   {
 174     int temp_len= ptr->prefix_key_length + key_length;
 175     char *temp= (char *)malloc(temp_len);
 176     strncpy(temp, ptr->prefix_key, ptr->prefix_key_length);
 177     strncpy(temp + ptr->prefix_key_length, key, key_length);
 178     hash= generate_hash(ptr, temp, temp_len);
 179     free(temp);
 180   }
 181   else
 182   {
 183     hash= generate_hash(ptr, key, key_length);
 184   }
 185
 186   WATCHPOINT_ASSERT(hash);
 187
 188   if (memcached_behavior_get(ptr, MEMCACHED_BEHAVIOR_AUTO_EJECT_HOSTS) && ptr->next_distribution_rebuild) {
 189     struct timeval now;
 190
 191     if (gettimeofday(&now, NULL) == 0 &&
 192         now.tv_sec > ptr->next_distribution_rebuild)
 193       run_distribution(ptr);
 194   }
 195
 196   return dispatch_host(ptr, hash);
 197 }
 198
 199 static uint32_t internal_generate_hash(const char *key, size_t key_length)
 200 {
 201   const char *ptr= key;
 202   uint32_t value= 0;
 203
 204   while (key_length--)
 205   {
 206     value += *ptr++;
 207     value += (value << 10);
 208     value ^= (value >> 6);
 209   }
 210   value += (value << 3);
 211   value ^= (value >> 11);
 212   value += (value << 15);
 213
 214   return value == 0 ? 1 : value;
 215 }
 216
 217 static uint32_t internal_generate_md5(const char *key, size_t key_length)
 218 {
 219   unsigned char results[16];
 220
 221   md5_signature((unsigned char*)key, (unsigned int)key_length, results);
 222
 223   return ((uint32_t) (results[3] & 0xFF) << 24)
 224     | ((uint32_t) (results[2] & 0xFF) << 16)
 225     | ((uint32_t) (results[1] & 0xFF) << 8)
 226     | (results[0] & 0xFF);
 227 }