Commit db0ea224 authored by Yedidya Feldblum's avatar Yedidya Feldblum Committed by Facebook Github Bot

Namespacing and comments in folly/Likely.h

Summary:
[Folly] Namespacing and comments in `folly/Likely.h`.

This adds `FOLLY_LIKELY` and `FOLLY_UNLIKELY`.

Reviewed By: Orvid

Differential Revision: D6636136

fbshipit-source-id: da93220201cabca91b4477ab98269a0febb735db
parent af28f118
/*
* Copyright 2017 Facebook, Inc.
* Copyright 2012-present Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
......@@ -14,19 +14,33 @@
* limitations under the License.
*/
/**
* Compiler hints to indicate the fast path of an "if" branch: whether
* the if condition is likely to be true or false.
*
* @author Tudor Bosman (tudorb@fb.com)
*/
#pragma once
#if __GNUC__
#define FOLLY_DETAIL_BUILTIN_EXPECT(b, t) (__builtin_expect(b, t))
#else
#define FOLLY_DETAIL_BUILTIN_EXPECT(b, t) b
#endif
// Likeliness annotations
//
// Useful when the author has better knowledge than the compiler of whether
// the branch condition is overwhelmingly likely to take a specific value.
//
// Useful when the author has better knowledge than the compiler of which code
// paths are designed as the fast path and which are designed as the slow path,
// and to force the compiler to optimize for the fast path, even when it is not
// overwhelmingly likely.
#define FOLLY_LIKELY(x) FOLLY_DETAIL_BUILTIN_EXPECT((x), 1)
#define FOLLY_UNLIKELY(x) FOLLY_DETAIL_BUILTIN_EXPECT((x), 0)
// Un-namespaced annotations
#undef LIKELY
#undef UNLIKELY
#if defined(__GNUC__) && __GNUC__ >= 4
#if defined(__GNUC__)
#define LIKELY(x) (__builtin_expect((x), 1))
#define UNLIKELY(x) (__builtin_expect((x), 0))
#else
......
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