gallium: Simple and efficient cache.

Fixed size hash table. Collisions are handled by simply destroying the
previous entry.

It hasn't received much testing yet.

1 files changed, 209 insertions, 0 deletions

diff --git a/src/gallium/auxiliary/util/u_cache.c b/src/gallium/auxiliary/util/u_cache.c
new file mode 100644
index 00000000000..69a52687fbc
--- /dev/null
+++ b/src/gallium/auxiliary/util/u_cache.c
@@ -0,0 +1,209 @@
+/**************************************************************************
+ *
+ * Copyright 2008 VMware, Inc.
+ * All Rights Reserved.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sub license, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the
+ * next paragraph) shall be included in all copies or substantial portions
+ * of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
+ * IN NO EVENT SHALL VMWARE AND/OR ITS SUPPLIERS BE LIABLE FOR
+ * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+ * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+ * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ *
+ **************************************************************************/
+
+/**
+ * @file
+ * Simple cache implementation.
+ *
+ * We simply have fixed size array, and destroy previous values on collision. 
+ * 
+ * @author Jose Fonseca <[email protected]>
+ */
+
+
+#include "pipe/p_compiler.h"
+#include "pipe/p_debug.h"
+
+#include "util/u_math.h"
+#include "util/u_memory.h"
+#include "util/u_cache.h"
+
+
+struct util_cache_entry
+{
+   void *key;
+   void *value;
+   
+#ifdef DEBUG
+   unsigned count;
+#endif
+};
+
+
+struct util_cache
+{
+   /** Hash function */
+   uint32_t (*hash)(void *key);
+   
+   /** Compare two keys */
+   int (*compare)(void *key1, void *key2);
+
+   /** Destroy a (key, value) pair */
+   void (*destroy)(void *key, void *value);
+
+   uint32_t size;
+   
+   struct util_cache_entry *entries;
+   
+#ifdef DEBUG
+   unsigned count;
+#endif
+};
+
+
+struct util_cache *
+util_cache_create(uint32_t (*hash)(void *key),
+                int (*compare)(void *key1, void *key2),
+                void (*destroy)(void *key, void *value),
+                uint32_t size)
+{
+   struct util_cache *cache;
+   
+   cache = CALLOC_STRUCT(util_cache);
+   if(!cache)
+      return NULL;
+   
+   cache->hash = hash;
+   cache->compare = compare;
+   cache->destroy = destroy;
+   cache->size = size;
+   
+   cache->entries = CALLOC(size, sizeof(struct util_cache_entry));
+   if(!cache->entries) {
+      FREE(cache);
+      return NULL;
+   }
+   
+   return cache;
+}
+
+
+static INLINE struct util_cache_entry *
+util_cache_entry_get(struct util_cache *cache,
+                     void *key)
+{
+   uint32_t hash;
+   
+   hash = cache->hash(key);
+
+   return &cache->entries[hash % cache->size];
+}
+
+static INLINE void
+util_cache_entry_destroy(struct util_cache *cache,
+                         struct util_cache_entry *entry)
+{
+   void *key = entry->key;
+   void *value = entry->value;
+   
+   entry->key = NULL;
+   entry->value = NULL;
+   
+   if(key || value)
+      if(cache->destroy)
+         cache->destroy(key, value);
+}
+
+
+void
+util_cache_set(struct util_cache *cache,
+               void *key,
+               void *value)
+{
+   struct util_cache_entry *entry;
+
+   assert(cache);
+
+   entry = util_cache_entry_get(cache, key);
+   util_cache_entry_destroy(cache, entry);
+   
+#ifdef DEBUG
+   ++entry->count;
+   ++cache->count;
+#endif
+   
+   entry->key = key;
+   entry->value = value;
+}
+
+
+void *
+util_cache_get(struct util_cache *cache, 
+               void *key)
+{
+   struct util_cache_entry *entry;
+
+   assert(cache);
+
+   entry = util_cache_entry_get(cache, key);
+   if(!entry->key && !entry->value)
+      return NULL;
+   
+   if(cache->compare(key, entry->key) != 0)
+      return NULL;
+   
+   return entry->value;
+}
+
+
+void 
+util_cache_clear(struct util_cache *cache)
+{
+   uint32_t i;
+
+   assert(cache);
+   
+   for(i = 0; i < cache->size; ++i)
+      util_cache_entry_destroy(cache, &cache->entries[i]);
+}
+
+
+void
+util_cache_destroy(struct util_cache *cache)
+{
+   assert(cache);
+
+#ifdef DEBUG
+   if(cache->count >= 20*cache->size) {
+      /* Normal approximation of the Poisson distribution */
+      double mean = (double)cache->count/(double)cache->size;
+      double stddev = sqrt(mean);
+      unsigned i;
+      for(i = 0; i < cache->size; ++i) {
+         double z = fabs(cache->count - mean)/stddev;
+         /* This assert should not fail 99.9999998027% of the times, unless 
+          * the hash function is a poor one */
+         assert(z <= 6.0);
+      }
+   }
+#endif
+      
+   util_cache_clear(cache);
+   
+   FREE(cache->entries);
+   FREE(cache);
+}