Add an LRU cache plus hashing primitives
This patch adds a hashtable-based LRU cache. This should be
significantly higher performance than the GenerationCache it is intended
to replace. It is a large part of the fix for bug 7271109
TextLayoutCache low-level performance issues.
We added a new method to BasicHashtable to detect when rehashing is
needed, because the internal linked list pointers would get invalidated
by that rehashing.
Also, the hash_type specialized to pointers had a small flaw.
Change-Id: I950c2083f96519777b851dbe157100e0a334caec
diff --git a/include/utils/JenkinsHash.h b/include/utils/JenkinsHash.h
new file mode 100644
index 0000000..e964e6f
--- /dev/null
+++ b/include/utils/JenkinsHash.h
@@ -0,0 +1,44 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/* Implementation of Jenkins one-at-a-time hash function. These choices are
+ * optimized for code size and portability, rather than raw speed. But speed
+ * should still be quite good.
+ **/
+
+#include <utils/TypeHelpers.h>
+
+namespace android {
+
+/* The Jenkins hash of a sequence of 32 bit words A, B, C is:
+ * Whiten(Mix(Mix(Mix(0, A), B), C)) */
+
+inline uint32_t JenkinsHashMix(uint32_t hash, uint32_t data) {
+ hash += data;
+ hash += (hash << 10);
+ hash ^= (hash >> 6);
+ return hash;
+}
+
+hash_t JenkinsHashWhiten(uint32_t hash);
+
+/* Helpful utility functions for hashing data in 32 bit chunks */
+uint32_t JenkinsHashMixBytes(uint32_t hash, const uint8_t* bytes, size_t size);
+
+uint32_t JenkinsHashMixShorts(uint32_t hash, const uint16_t* shorts, size_t size);
+
+}
+