X-Git-Url: https://git.m6w6.name/?a=blobdiff_plain;f=libmemcached%2Fmurmur_hash.c;h=edb9e7772afe8191801185aff9f8ae393b3440da;hb=7b548d21a8eafec0b830ad1bd6429cecd4eaeba8;hp=abb2deda3e5340f68cc04e7dc4b6dd8f4da8b930;hpb=34a8c3858f30b02568c87f56a827f618aba6d6be;p=awesomized%2Flibmemcached

diff --git a/libmemcached/murmur_hash.c b/libmemcached/murmur_hash.c
index abb2deda..edb9e777 100644
--- a/libmemcached/murmur_hash.c
+++ b/libmemcached/murmur_hash.c
@@ -1,48 +1,76 @@
-#include "common.h"
-
-/* 
-  "Murmur"hash provided by Austin, tanjent@gmail.com
-#define MURMUR_POSTMIX
-*/
-
-uint32_t murmur_hash(char *key, size_t length)
-{
-  const unsigned int m= 0x7fd652ad;
-  const int r= 16;
-
-  uint32_t h= 0xdeadbeef;
-
-  while(length >= 4)
-  {
-    h += *(unsigned int *)key;
-    h *= m;
-    h ^= h >> r;
-
-    key += 4;
-    length -= 4;
-  }
-
-  switch(length)
-  {
-  case 3:
-    h += key[2] << 16;
-  case 2:
-    h += key[1] << 8;
-  case 1:
-  default:
-    h += key[0];
-    h *= m;
-    h ^= h >> r;
-  };
-
-#ifdef MURMUR_POSTMIX
-
-  h *= m;
-  h ^= h >> 10;
-  h *= m;
-  h ^= h >> 17;
-
-#endif
-
-  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 unsigned int seed= (0xdeadbeef * length);
+  const int r= 24;
+
+
+  // Initialize the hash to a 'random' value
+
+  unsigned int h= seed ^ 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 ^= data[2] << 16;
+  case 2: h ^= 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 h;
+}