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.

4 files changed, 102 insertions, 87 deletions

diff --git a/libdiskfs/name-cache.c b/libdiskfs/name-cache.c
index e9fe27ea..53935ab3 100644
--- a/libdiskfs/name-cache.c
+++ b/libdiskfs/name-cache.c
@@ -21,6 +21,7 @@
 
 #include "priv.h"
 #include <assert.h>
+#include <hurd/ihash.h>
 #include <string.h>
 
 /* The name cache is implemented using a hash table.
@@ -118,90 +119,6 @@ valid_entry (struct cache_bucket *b, int i)
   return b->name[i] != 0;
 }
 
-/* This is the Murmur3 hash algorithm.  */
-
-#define FORCE_INLINE inline __attribute__((always_inline))
-
-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.  */
-void MurmurHash3_x86_32 ( const void * key, int len,
-                          uint32_t seed, void * out )
-{
-  const uint8_t * data = (const uint8_t*)key;
-  const int nblocks = 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);
-
-  *(uint32_t*)out = h1;
-}
-
 /* If there is no best candidate to replace, pick any.  We approximate
    any by picking the slot depicted by REPLACE, and increment REPLACE
    then.  */
@@ -259,8 +176,8 @@ static inline unsigned long
 hash (ino64_t dir_cache_id, const char *name)
 {
   unsigned long h;
-  MurmurHash3_x86_32 (&dir_cache_id, sizeof dir_cache_id, 0, &h);
-  MurmurHash3_x86_32 (name, strlen (name), h, &h);
+  h = hurd_ihash_hash32 (&dir_cache_id, sizeof dir_cache_id, 0);
+  h = hurd_ihash_hash32 (name, strlen (name), h);
   return h;
 }
 
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")));