Added MurmurHash for string hashing (not used yet).

upb_table.c

@@ -10,6 +10,180 @@
 #include <stdlib.h>
 #include <string.h>
 
+#ifdef UPB_UNALIGNED_READS_OK
+//-----------------------------------------------------------------------------
+// MurmurHash2, by Austin Appleby
+// Reformatted and C99-ified by Joshua Haberman.
+// 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
+//   2. sizeof(int) == 4 (in upb this limitation is removed by using uint32_t
+// 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.
+static uint32_t MurmurHash2(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 uint32_t m = 0x5bd1e995;
+  const int32_t r = 24;
+
+  // Initialize the hash to a 'random' value
+  uint32_t h = seed ^ len;
+
+  // Mix 4 bytes at a time into the hash
+  const uint8_t * data = (const uint8_t *)key;
+  while(len >= 4) {
+    uint32_t k = *(uint32_t *)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;
+}
+
+#else // !UPB_UNALIGNED_READS_OK
+
+//-----------------------------------------------------------------------------
+// MurmurHashAligned2, by Austin Appleby
+// Same algorithm as MurmurHash2, but only does aligned reads - should be safer
+// on certain platforms.
+// Performance will be lower than MurmurHash2
+
+#define MIX(h,k,m) { k *= m; k ^= k >> r; k *= m; h *= m; h ^= k; }
+
+static uint32_t MurmurHash2(const void * key, size_t len, uint32_t seed)
+{
+  const uint32_t m = 0x5bd1e995;
+  const int32_t r = 24;
+  const uint8_t * data = (const uint8_t *)key;
+  uint32_t h = seed ^ len;
+  uint8_t align = (uintptr_t)data & 3;
+
+  if(align && (len >= 4)) {
+    // Pre-load the temp registers
+    uint32_t t = 0, d = 0;
+
+    switch(align) {
+      case 1: t |= data[2] << 16;
+      case 2: t |= data[1] << 8;
+      case 3: t |= data[0];
+    }
+
+    t <<= (8 * align);
+
+    data += 4-align;
+    len -= 4-align;
+
+    int32_t sl = 8 * (4-align);
+    int32_t sr = 8 * align;
+
+    // Mix
+
+    while(len >= 4) {
+      d = *(uint32_t *)data;
+      t = (t >> sr) | (d << sl);
+
+      uint32_t k = t;
+
+      MIX(h,k,m);
+
+      t = d;
+
+      data += 4;
+      len -= 4;
+    }
+
+    // Handle leftover data in temp registers
+
+    d = 0;
+
+    if(len >= align) {
+      switch(align) {
+        case 3: d |= data[2] << 16;
+        case 2: d |= data[1] << 8;
+        case 1: d |= data[0];
+      }
+
+      uint32_t k = (t >> sr) | (d << sl);
+      MIX(h,k,m);
+
+      data += align;
+      len -= align;
+
+      //----------
+      // Handle tail bytes
+
+      switch(len) {
+        case 3: h ^= data[2] << 16;
+        case 2: h ^= data[1] << 8;
+        case 1: h ^= data[0]; h *= m;
+      };
+    } else {
+      switch(len) {
+        case 3: d |= data[2] << 16;
+        case 2: d |= data[1] << 8;
+        case 1: d |= data[0];
+        case 0: h ^= (t >> sr) | (d << sl); h *= m;
+      }
+    }
+
+    h ^= h >> 13;
+    h *= m;
+    h ^= h >> 15;
+
+    return h;
+  } else {
+    while(len >= 4) {
+      uint32_t k = *(uint32_t *)data;
+
+      MIX(h,k,m);
+
+      data += 4;
+      len -= 4;
+    }
+
+    //----------
+    // Handle tail bytes
+
+    switch(len) {
+      case 3: h ^= data[2] << 16;
+      case 2: h ^= data[1] << 8;
+      case 1: h ^= data[0]; h *= m;
+    };
+
+    h ^= h >> 13;
+    h *= m;
+    h ^= h >> 15;
+
+    return h;
+  }
+}
+#undef MIX
+
+#endif // UPB_UNALIGNED_READS_OK
+
 static int compare_entries(const void *f1, const void *f2)
 {
   return ((struct upb_inttable_entry*)f1)->key -
@@ -120,4 +294,3 @@ void upb_inttable_free(struct upb_inttable *table)
   free(table->entries);
 }
 
-/* Emit definition for inline functions. */

upb_table.h

@@ -2,6 +2,14 @@
  * upb - a minimalist implementation of protocol buffers.
  *
  * Copyright (c) 2009 Joshua Haberman.  See LICENSE for details.
+ *
+ * This file defines very fast int->struct (inttable) and string->struct
+ * (strtable) hash tables.  The struct can be of any size, and it is stored
+ * in the table itself, for cache-friendly performance.
+ *
+ * The table uses internal chaining with Brent's variation (inspired by the
+ * Lua implementation of hash tables).  The hash function for strings is
+ * Austin Appleby's "MurmurHash."
  */
 
 #ifndef UPB_TABLE_H_