Make hash table algorithm selectable

jenkins hash is old. Lets try murmur3 to start! Default is the old one, so
people aren't surprised.

1 files changed, 124 insertions, 0 deletions

diff --git a/murmur3_hash.c b/murmur3_hash.c
new file mode 100644
index 0000000..4aa4f93
--- /dev/null
+++ b/murmur3_hash.c
@@ -0,0 +1,124 @@
+//-----------------------------------------------------------------------------
+// MurmurHash3 was written by Austin Appleby, and is placed in the public
+// domain. The author hereby disclaims copyright to this source code.
+
+// Note - The x86 and x64 versions do _not_ produce the same results, as the
+// algorithms are optimized for their respective platforms. You can still
+// compile and run any of them on any platform, but your performance with the
+// non-native version will be less than optimal.
+
+#include "murmur3_hash.h"
+
+//-----------------------------------------------------------------------------
+// Platform-specific functions and macros
+
+// Microsoft Visual Studio
+
+#if defined(_MSC_VER)
+
+#define FORCE_INLINE    __forceinline
+
+#include <stdlib.h>
+
+#define ROTL32(x,y)    _rotl(x,y)
+
+#define BIG_CONSTANT(x) (x)
+
+// Other compilers
+
+#else    // defined(_MSC_VER)
+
+#define    FORCE_INLINE inline __attribute__((always_inline))
+
+static inline uint32_t rotl32 ( uint32_t x, int8_t r )
+{
+  return (x << r) | (x >> (32 - r));
+}
+
+#define    ROTL32(x,y)    rotl32(x,y)
+
+#define BIG_CONSTANT(x) (x##LLU)
+
+#endif // !defined(_MSC_VER)
+
+//-----------------------------------------------------------------------------
+// Block read - if your platform needs to do endian-swapping or can only
+// handle aligned reads, do the conversion here
+
+static FORCE_INLINE uint32_t getblock32 ( const uint32_t * p, int i )
+{
+  return p[i];
+}
+
+//-----------------------------------------------------------------------------
+// Finalization mix - force all bits of a hash block to avalanche
+
+static FORCE_INLINE uint32_t fmix32 ( uint32_t h )
+{
+  h ^= h >> 16;
+  h *= 0x85ebca6b;
+  h ^= h >> 13;
+  h *= 0xc2b2ae35;
+  h ^= h >> 16;
+
+  return h;
+}
+
+//-----------------------------------------------------------------------------
+
+/* Defintion modified slightly from the public domain interface (no seed +
+ * return value */
+uint32_t MurmurHash3_x86_32 ( const void * key, size_t length)
+{
+  const uint8_t * data = (const uint8_t*)key;
+  const int nblocks = length / 4;
+
+  uint32_t h1 = 0;
+
+  uint32_t c1 = 0xcc9e2d51;
+  uint32_t c2 = 0x1b873593;
+
+  //----------
+  // body
+
+  const uint32_t * blocks = (const uint32_t *)(data + nblocks*4);
+
+  for(int i = -nblocks; i; i++)
+  {
+    uint32_t k1 = getblock32(blocks,i);
+
+    k1 *= c1;
+    k1 = ROTL32(k1,15);
+    k1 *= c2;
+
+    h1 ^= k1;
+    h1 = ROTL32(h1,13);
+    h1 = h1*5+0xe6546b64;
+  }
+
+  //----------
+  // tail
+
+  const uint8_t * tail = (const uint8_t*)(data + nblocks*4);
+
+  uint32_t k1 = 0;
+
+  switch(length & 3)
+  {
+  case 3: k1 ^= tail[2] << 16;
+  case 2: k1 ^= tail[1] << 8;
+  case 1: k1 ^= tail[0];
+          k1 *= c1; k1 = ROTL32(k1,15); k1 *= c2; h1 ^= k1;
+  };
+
+  //----------
+  // finalization
+
+  h1 ^= length;
+
+  h1 = fmix32(h1);
+
+  //*(uint32_t*)out = h1;
+  return h1;
+}
+