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
42template <int (*cmp)(const char* l, const char* r, const size_t s)>
43static 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
49template <int (*cmp)(const char* l, const char* r, const size_t s)>
50static 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
56template <int (*cmp)(const void* l, const void* r, const size_t s)>
57static 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
65template <int (*cmp)(const char* l, const char* r)>
66static inline int fastcmp(const char* l, const char* r) {
67    return (*l != *r) || (__predict_true(*l) && cmp(l + 1, r + 1));
68}
69
70template <int (*cmp)(const char* l, const char* r)>
71static 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