now creating a linkable library

1 files changed, 69 insertions, 0 deletions

diff --git a/vowpalwabbit/hash.cc b/vowpalwabbit/hash.cc
new file mode 100644
index 00000000..429ea187
--- /dev/null
+++ b/vowpalwabbit/hash.cc
@@ -0,0 +1,69 @@
+// Tweaked for VW and contributed by Ariel Faigon.
+// Original at: http://murmurhash.googlepages.com/
+//
+// Based on MurmurHash2, by Austin Appleby
+//
+// 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
+//    (i.e non aligned access is supported) - this is not a problem
+//    on Intel/x86/AMD64 machines (including new Macs)
+// 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.
+//
+#include <stdint.h>	/* defines uint32_t etc */
+#include <sys/types.h>	/* defines size_t */
+
+#define MIX(h,k,m) { k *= m; k ^= k >> r; k *= m; h *= m; h ^= k; }
+
+uint32_t uniform_hash( const void *key, size_t len, uint32_t seed)
+{
+    // '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 int r = 24;
+
+    // Initialize the hash to a 'random' value
+
+    unsigned int h = seed ^ len;
+
+    // Mix 4 bytes at a time into the hash
+
+    const unsigned char * data = (const unsigned char *)key;
+
+    while (len >= 4) {
+	unsigned int k = *(unsigned int *)data;
+
+	k *= m;
+	k ^= k >> r;
+	k *= m;
+
+	h *= m;
+	h ^= k;
+
+	data += 4;
+	len -= 4;
+    }
+
+    // Handle the last few bytes of the input array
+    switch (len) {
+	case 3: h ^= data[2] << 16;
+	case 2: h ^= data[1] << 8;
+	case 1: h ^= data[0];
+		h *= m;
+    };
+
+    // 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;
+}
+