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.

3 files changed, 99 insertions, 1 deletions

diff --git a/libihash/Makefile b/libihash/Makefile
index 09bb1362..3377ef41 100644
--- a/libihash/Makefile
+++ b/libihash/Makefile
@@ -20,7 +20,7 @@ dir := libihash
 makemode := library
 
 libname := libihash
-SRCS = ihash.c
+SRCS = ihash.c murmur3.c
 installhdrs = ihash.h
 
 OBJS = $(SRCS:.c=.o)
diff --git a/libihash/ihash.h b/libihash/ihash.h
index 28fefe80..356f6473 100644
--- a/libihash/ihash.h
+++ b/libihash/ihash.h
@@ -349,5 +349,10 @@ int hurd_ihash_remove (hurd_ihash_t ht, hurd_ihash_key_t key);
    was provided to hurd_ihash_add().  This call is faster than
    hurd_ihash_remove().  */
 void hurd_ihash_locp_remove (hurd_ihash_t ht, hurd_ihash_locp_t locp);
+
+/* We provide a general purpose hash function.  This function can be
+   used with the generalized key interface to use arbitrary data as
+   keys using this library.  */
+uint32_t hurd_ihash_hash32 (const void *buf, size_t len, uint32_t seed);
 
 #endif	/* _HURD_IHASH_H */
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")));