utils: Add FastStrcmp.h
Move existing fast<str*cmp> templates for general use, pulled from
the implementation used in logd that dealt with speed through cache
locality and subroutine call mitigation. Rename to fastcmp.
Test: logd-benchmarks and based on manual profiling from the past
Bug: 31456426
Change-Id: Ic62f4a437fc3e06ffdeaae73a6f34e197957a6b0
diff --git a/include/utils/FastStrcmp.h b/include/utils/FastStrcmp.h
new file mode 100644
index 0000000..3844e7d
--- /dev/null
+++ b/include/utils/FastStrcmp.h
@@ -0,0 +1,54 @@
+/*
+ * Copyright (C) 2014-2016 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.
+ */
+
+#ifndef _ANDROID_UTILS_FASTSTRCMP_H__
+#define _ANDROID_UTILS_FASTSTRCMP_H__
+
+#ifdef __cplusplus
+
+// Optimized for instruction cache locality
+//
+// Template class fastcmp used to create more time-efficient str*cmp
+// functions by pre-checking the first character before resorting
+// to calling the underlying string function. Profiled with a
+// measurable speedup when used in hot code. Usage is of the form:
+//
+// fastcmp<strncmp>(str1, str2, len)
+//
+// NB: Does not work for the case insensitive str*cmp functions.
+// NB: Returns boolean, do not use if expecting to check negative value.
+// Thus not semantically identical to the expected function behavior.
+
+template <int (*cmp)(const char *l, const char *r, const size_t s)>
+static inline int fastcmp(const char *l, const char *r, const size_t s) {
+ return (*l != *r) || cmp(l + 1, r + 1, s - 1);
+}
+
+template <int (*cmp)(const void *l, const void *r, const size_t s)>
+static inline int fastcmp(const void *lv, const void *rv, const size_t s) {
+ const char *l = static_cast<const char *>(lv);
+ const char *r = static_cast<const char *>(rv);
+ return (*l != *r) || cmp(l + 1, r + 1, s - 1);
+}
+
+template <int (*cmp)(const char *l, const char *r)>
+static inline int fastcmp(const char *l, const char *r) {
+ return (*l != *r) || cmp(l + 1, r + 1);
+}
+
+#endif
+
+#endif // _ANDROID_UTILS_FASTSTRCMP_H__