util/hash_table: Pull the details of the FNV-1a into helpers

This way the basics of the FNV-1a hash can be reused to easily create other
hashing functions.

Reviewed-by: Eric Anholt <eric@anholt.net>

src/util/hash_table.c

@@ -431,27 +431,18 @@ _mesa_hash_table_random_entry(struct hash_table *ht,
 uint32_t
 _mesa_hash_data(const void *data, size_t size)
 {
-   uint32_t hash = 2166136261ul;
-   const uint8_t *bytes = data;
-
-   while (size-- != 0) {
-      hash ^= *bytes;
-      hash = hash * 0x01000193;
-      bytes++;
-   }
-
-   return hash;
+   return _mesa_fnv32_1a_accumulate_block(_mesa_fnv32_1a_offset_bias,
+                                          data, size);
 }
 
 /** FNV-1a string hash implementation */
 uint32_t
 _mesa_hash_string(const char *key)
 {
-   uint32_t hash = 2166136261ul;
+   uint32_t hash = _mesa_fnv32_1a_offset_bias;
 
    while (*key != 0) {
-      hash ^= *key;
-      hash = hash * 0x01000193;
+      hash = _mesa_fnv32_1a_accumulate(hash, *key);
       key++;
    }
 

src/util/hash_table.h

@@ -101,6 +101,25 @@ static inline uint32_t _mesa_hash_pointer(const void *pointer)
    return _mesa_hash_data(&pointer, sizeof(pointer));
 }
 
+static const uint32_t _mesa_fnv32_1a_offset_bias = 2166136261u;
+
+static inline uint32_t
+_mesa_fnv32_1a_accumulate_block(uint32_t hash, const void *data, size_t size)
+{
+   const uint8_t *bytes = (const uint8_t *)data;
+
+   while (size-- != 0) {
+      hash ^= *bytes;
+      hash = hash * 0x01000193;
+      bytes++;
+   }
+
+   return hash;
+}
+
+#define _mesa_fnv32_1a_accumulate(hash, expr) \
+   _mesa_fnv32_1a_accumulate_block(hash, &(expr), sizeof(expr))
+
 /**
  * This foreach function is safe against deletion (which just replaces
  * an entry's data with the deleted marker), but not against insertion