1/*
2 * Copyright 2011-present Facebook, Inc.
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#pragma once
18
19#if __GNUC__
20#define FOLLY_DETAIL_BUILTIN_EXPECT(b, t) (__builtin_expect(b, t))
21#else
22#define FOLLY_DETAIL_BUILTIN_EXPECT(b, t) b
23#endif
24
25// Likeliness annotations
26//
27// Useful when the author has better knowledge than the compiler of whether
28// the branch condition is overwhelmingly likely to take a specific value.
29//
30// Useful when the author has better knowledge than the compiler of which code
31// paths are designed as the fast path and which are designed as the slow path,
32// and to force the compiler to optimize for the fast path, even when it is not
33// overwhelmingly likely.
34
35#define FOLLY_LIKELY(x) FOLLY_DETAIL_BUILTIN_EXPECT((x), 1)
36#define FOLLY_UNLIKELY(x) FOLLY_DETAIL_BUILTIN_EXPECT((x), 0)
37
38// Un-namespaced annotations
39
40#undef LIKELY
41#undef UNLIKELY
42
43#if defined(__GNUC__)
44#define LIKELY(x) (__builtin_expect((x), 1))
45#define UNLIKELY(x) (__builtin_expect((x), 0))
46#else
47#define LIKELY(x) (x)
48#define UNLIKELY(x) (x)
49#endif
50