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)>
fastcmp(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)>
fasticmp(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)>
fastcmp(const void * lv,const void * rv,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)>
fastcmp(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)>
fasticmp(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