summaryrefslogtreecommitdiff
path: root/libihash/murmur3.c
diff options
context:
space:
mode:
authorJustus Winter <4winter@informatik.uni-hamburg.de>2015-11-27 03:24:24 +0100
committerJustus Winter <4winter@informatik.uni-hamburg.de>2015-11-29 23:57:56 +0100
commit4e2d5a81bb2834f7393e9847bfa091f8a0a07556 (patch)
tree87eb878db4a269948a39566f14be9315733f5919 /libihash/murmur3.c
parent1842a9dcd1056dac886e96071e8c5dcd2859d471 (diff)
libihash: provide a general purpose hash algorithm
* libdiskfs/name-cache.c: Move the Murmur3 algorithm... * libihash/murmur3.c: ... here, and properly attribute the code. * libihash/ihash.h (hurd_ihash_hash32): New prototype. * libihash/Makefile (SRCS): Add new file.
Diffstat (limited to 'libihash/murmur3.c')
-rw-r--r--libihash/murmur3.c93
1 files changed, 93 insertions, 0 deletions
diff --git a/libihash/murmur3.c b/libihash/murmur3.c
new file mode 100644
index 00000000..e45180a4
--- /dev/null
+++ b/libihash/murmur3.c
@@ -0,0 +1,93 @@
+/* This is the Murmur3 hash algorithm.
+ *
+ * MurmurHash3 was written by Austin Appleby, and is placed in the public
+ * domain. The author hereby disclaims copyright to this source code.
+ */
+
+#include <stdint.h>
+#include <stdio.h>
+
+#define FORCE_INLINE static 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)
+
+/* Block read - if your platform needs to do endian-swapping or can
+ only handle aligned reads, do the conversion here. */
+
+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. */
+
+FORCE_INLINE uint32_t fmix32 ( uint32_t h )
+{
+ h ^= h >> 16;
+ h *= 0x85ebca6b;
+ h ^= h >> 13;
+ h *= 0xc2b2ae35;
+ h ^= h >> 16;
+
+ return h;
+}
+
+/* The Murmur3 hash function. */
+static uint32_t
+MurmurHash3_x86_32 (const void *key, size_t len, uint32_t seed)
+{
+ const uint8_t * data = (const uint8_t*)key;
+ const int nblocks = (int) (len / 4);
+
+ uint32_t h1 = seed;
+
+ const uint32_t c1 = 0xcc9e2d51;
+ const 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(len & 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 ^= len;
+
+ h1 = fmix32(h1);
+
+ return h1;
+}
+
+uint32_t hurd_ihash_hash32 (const void *, size_t, uint32_t)
+ __attribute__ ((weak, alias ("MurmurHash3_x86_32")));