X-Git-Url: https://git.m6w6.name/?a=blobdiff_plain;f=libmemcached%2Fmurmur_hash.c;h=f1c3267c53844ee903889d913fba3e0f8b95797d;hb=c204651e1ee8185224ccc78bd68801ab43740844;hp=7cfcaa9eba087559de5c2d371f85bec615c6c460;hpb=1d7f999b7d38db3308a0533a83fea23987fb0178;p=awesomized%2Flibmemcached

diff --git a/libmemcached/murmur_hash.c b/libmemcached/murmur_hash.c
index 7cfcaa9e..f1c3267c 100644
--- a/libmemcached/murmur_hash.c
+++ b/libmemcached/murmur_hash.c
@@ -1,39 +1,76 @@
-#include "common.h"
-
-/* 
-  "Murmur"hash provided by Austin, tanjent@gmail.com
-*/
-
-#define MIX(h,k,m) { k *= m; k ^= k >> r; k *= m; h *= m; h ^= k; }
-
-uint32_t murmur_hash(char *key, size_t length)
-{
-  const uint32_t m= 0x5bd1e995;
-  const int r= 16;
-  uint32_t h= length * m;
-  uint32_t k = 0;
-
-  while(length >= 4)
-  {
-    k = *(uint32_t*)key;
-    MIX(h,k,m);
-
-    key += 4;
-    length -= 4;
-  }
-
-  switch(length)
-  {
-  case 3: k += key[2] << 16;
-  case 2: k += key[1] << 8;
-  case 1: k += key[0];
-          MIX(h,k,m);
-  };
-
-  h *= m;
-  h ^= h >> 10;
-  h *= m;
-  h ^= h >> 17;
-
-  return h;
-}
+/* 
+  "Murmur" hash provided by Austin, tanjent@gmail.com
+  http://murmurhash.googlepages.com/
+
+  Note - This code makes a few assumptions about how your machine behaves -
+
+  1. We can read a 4-byte value from any address without crashing
+  2. sizeof(int) == 4
+
+  And it has a few limitations -
+  1. It will not work incrementally.
+  2. It will not produce the same results on little-endian and big-endian
+  machines.
+
+  Updated to murmur2 hash - BP
+*/
+
+#include "common.h"
+
+uint32_t murmur_hash(const char *key, size_t length)
+{
+  /* 
+    'm' and 'r' are mixing constants generated offline.  They're not
+    really 'magic', they just happen to work well.
+  */
+
+  const unsigned int m= 0x5bd1e995;
+  const uint32_t seed= (0xdeadbeef * (uint32_t)length);
+  const int r= 24;
+
+
+  // Initialize the hash to a 'random' value
+
+  uint32_t h= seed ^ (uint32_t)length;
+
+  // Mix 4 bytes at a time into the hash
+
+  const unsigned char * data= (const unsigned char *)key;
+
+  while(length >= 4)
+  {
+    unsigned int k = *(unsigned int *)data;
+
+    k *= m; 
+    k ^= k >> r; 
+    k *= m; 
+
+    h *= m; 
+    h ^= k;
+
+    data += 4;
+    length -= 4;
+  }
+
+  // Handle the last few bytes of the input array
+
+  switch(length)
+  {
+  case 3: h ^= ((uint32_t)data[2]) << 16;
+  case 2: h ^= ((uint32_t)data[1]) << 8;
+  case 1: h ^= data[0];
+          h *= m;
+  default: break;
+  };
+
+  /* 
+    Do a few final mixes of the hash to ensure the last few bytes are
+    well-incorporated.  
+  */
+
+  h ^= h >> 13;
+  h *= m;
+  h ^= h >> 15;
+
+  return (uint32_t) h;
+}