1 /* 2 * Copyright (C) 2014-2016 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #ifndef _ANDROID_UTILS_FASTSTRCMP_H__ 18 #define _ANDROID_UTILS_FASTSTRCMP_H__ 19 20 #include <ctype.h> 21 #include <string.h> 22 23 #ifndef __predict_true 24 #define __predict_true(exp) __builtin_expect((exp) != 0, 1) 25 #endif 26 27 #ifdef __cplusplus 28 29 // Optimized for instruction cache locality 30 // 31 // Template class fastcmp used to create more time-efficient str*cmp 32 // functions by pre-checking the first character before resorting 33 // to calling the underlying string function. Profiled with a 34 // measurable speedup when used in hot code. Usage is of the form: 35 // 36 // fastcmp<strncmp>(str1, str2, len) 37 // 38 // NB: use fasticmp for the case insensitive str*cmp functions. 39 // NB: Returns boolean, do not use if expecting to check negative value. 40 // Thus not semantically identical to the expected function behavior. 41 42 template <int (*cmp)(const char* l, const char* r, const size_t s)> 43 static inline int fastcmp(const char* l, const char* r, const size_t s) { 44 const ssize_t n = s; // To help reject negative sizes, treat like zero 45 return __predict_true(n > 0) && 46 ((*l != *r) || (__predict_true(n > 1) && cmp(l + 1, r + 1, n - 1))); 47 } 48 49 template <int (*cmp)(const char* l, const char* r, const size_t s)> 50 static inline int fasticmp(const char* l, const char* r, const size_t s) { 51 const ssize_t n = s; // To help reject negative sizes, treat like zero 52 return __predict_true(n > 0) && 53 ((tolower(*l) != tolower(*r)) || (__predict_true(n > 1) && cmp(l + 1, r + 1, n - 1))); 54 } 55 56 template <int (*cmp)(const void* l, const void* r, const size_t s)> 57 static inline int fastcmp(const void* lv, const void* rv, const size_t s) { 58 const char* l = static_cast<const char*>(lv); 59 const char* r = static_cast<const char*>(rv); 60 const ssize_t n = s; // To help reject negative sizes, treat like zero 61 return __predict_true(n > 0) && 62 ((*l != *r) || (__predict_true(n > 1) && cmp(l + 1, r + 1, n - 1))); 63 } 64 65 template <int (*cmp)(const char* l, const char* r)> 66 static inline int fastcmp(const char* l, const char* r) { 67 return (*l != *r) || (__predict_true(*l) && cmp(l + 1, r + 1)); 68 } 69 70 template <int (*cmp)(const char* l, const char* r)> 71 static inline int fasticmp(const char* l, const char* r) { 72 return (tolower(*l) != tolower(*r)) || (__predict_true(*l) && cmp(l + 1, r + 1)); 73 } 74 75 #endif 76 77 #endif // _ANDROID_UTILS_FASTSTRCMP_H__ 78
