77 lines
2.1 KiB
C
77 lines
2.1 KiB
C
/*
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* Copyright (c) Meta Platforms, Inc. and affiliates.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/**
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* Likeliness annotations.
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*
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* Useful when the author has better knowledge than the compiler of whether
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* the branch condition is overwhelmingly likely to take a specific value.
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*
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* Useful when the author has better knowledge than the compiler of which code
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* paths are designed as the fast path and which are designed as the slow path,
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* and to force the compiler to optimize for the fast path, even when it is not
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* overwhelmingly likely.
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*
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* Notes:
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* * All supported compilers treat unconditionally-noreturn blocks as unlikely.
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* This is true for blocks which unconditionally throw exceptions and for
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* blocks which unconditionally call [[noreturn]]-annotated functions. Such
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* cases do not require likeliness annotations.
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*
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* @file Likely.h
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* @refcode folly/docs/examples/folly/Likely.cpp
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*/
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#pragma once
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#include <folly/lang/Builtin.h>
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/**
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* Treat the condition as likely.
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*
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* @def FOLLY_LIKELY
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*/
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#define FOLLY_LIKELY(...) FOLLY_BUILTIN_EXPECT((__VA_ARGS__), 1)
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/**
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* Treat the condition as unlikely.
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*
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* @def FOLLY_UNLIKELY
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*/
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#define FOLLY_UNLIKELY(...) FOLLY_BUILTIN_EXPECT((__VA_ARGS__), 0)
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// Un-namespaced annotations
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#undef LIKELY
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#undef UNLIKELY
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/**
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* Treat the condition as likely.
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*
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* @def LIKELY
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*/
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/**
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* Treat the condition as unlikely.
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*
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* @def UNLIKELY
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*/
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#if defined(__GNUC__)
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#define LIKELY(x) (__builtin_expect((x), 1))
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#define UNLIKELY(x) (__builtin_expect((x), 0))
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#else
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#define LIKELY(x) (x)
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#define UNLIKELY(x) (x)
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#endif
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