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56 lines
2.5 KiB
C++
56 lines
2.5 KiB
C++
#ifndef RUBY_BACKWARD2_ASSUME_H /*-*-C++-*-vi:se ft=cpp:*/
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#define RUBY_BACKWARD2_ASSUME_H
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/**
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* @file
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* @author Ruby developers <ruby-core@ruby-lang.org>
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* @copyright This file is a part of the programming language Ruby.
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* Permission is hereby granted, to either redistribute and/or
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* modify this file, provided that the conditions mentioned in the
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* file COPYING are met. Consult the file for details.
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* @warning Symbols prefixed with either `RBIMPL` or `rbimpl` are
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* implementation details. Don't take them as canon. They could
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* rapidly appear then vanish. The name (path) of this header file
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* is also an implementation detail. Do not expect it to persist
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* at the place it is now. Developers are free to move it anywhere
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* anytime at will.
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* @note To ruby-core: remember that this header can be possibly
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* recursively included from extension libraries written in C++.
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* Do not expect for instance `__VA_ARGS__` is always available.
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* We assume C99 for ruby itself but we don't assume languages of
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* extension libraries. They could be written in C++98.
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* @brief Defines #ASSUME / #RB_LIKELY / #UNREACHABLE
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*/
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#include "ruby/internal/config.h"
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#include "ruby/internal/assume.h"
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#include "ruby/internal/has/builtin.h"
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#define ASSUME RBIMPL_ASSUME /**< @old{RBIMPL_ASSUME} */
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#define UNREACHABLE RBIMPL_UNREACHABLE() /**< @old{RBIMPL_UNREACHABLE} */
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#define UNREACHABLE_RETURN RBIMPL_UNREACHABLE_RETURN /**< @old{RBIMPL_UNREACHABLE_RETURN} */
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/* likely */
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#if RBIMPL_HAS_BUILTIN(__builtin_expect)
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/**
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* Asserts that the given Boolean expression likely holds.
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*
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* @param x An expression that likely holds.
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*
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* @note Consider this macro carefully. It has been here since when CPUs were
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* like babies, but contemporary processors are beasts. They are
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* smarter than mare mortals like us today. Their branch predictions
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* highly expectedly outperform your use of this macro.
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*/
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# define RB_LIKELY(x) (__builtin_expect(!!(x), 1))
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/**
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* Asserts that the given Boolean expression likely doesn't hold.
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*
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* @param x An expression that likely doesn't hold.
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*/
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# define RB_UNLIKELY(x) (__builtin_expect(!!(x), 0))
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#else
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# define RB_LIKELY(x) (x)
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# define RB_UNLIKELY(x) (x)
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#endif
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#endif /* RUBY_BACKWARD2_ASSUME_H */
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