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Diffstat (limited to 'include/ruby/backward/2/assume.h')
| -rw-r--r-- | include/ruby/backward/2/assume.h | 56 |
1 files changed, 56 insertions, 0 deletions
diff --git a/include/ruby/backward/2/assume.h b/include/ruby/backward/2/assume.h new file mode 100644 index 0000000000..d148710127 --- /dev/null +++ b/include/ruby/backward/2/assume.h @@ -0,0 +1,56 @@ +#ifndef RUBY_BACKWARD2_ASSUME_H /*-*-C++-*-vi:se ft=cpp:*/ +#define RUBY_BACKWARD2_ASSUME_H +/** + * @file + * @author Ruby developers <ruby-core@ruby-lang.org> + * @copyright This file is a part of the programming language Ruby. + * Permission is hereby granted, to either redistribute and/or + * modify this file, provided that the conditions mentioned in the + * file COPYING are met. Consult the file for details. + * @warning Symbols prefixed with either `RBIMPL` or `rbimpl` are + * implementation details. Don't take them as canon. They could + * rapidly appear then vanish. The name (path) of this header file + * is also an implementation detail. Do not expect it to persist + * at the place it is now. Developers are free to move it anywhere + * anytime at will. + * @note To ruby-core: remember that this header can be possibly + * recursively included from extension libraries written in C++. + * Do not expect for instance `__VA_ARGS__` is always available. + * We assume C99 for ruby itself but we don't assume languages of + * extension libraries. They could be written in C++98. + * @brief Defines #ASSUME / #RB_LIKELY / #UNREACHABLE + */ +#include "ruby/internal/config.h" +#include "ruby/internal/assume.h" +#include "ruby/internal/has/builtin.h" + +#define ASSUME RBIMPL_ASSUME /**< @old{RBIMPL_ASSUME} */ +#define UNREACHABLE RBIMPL_UNREACHABLE() /**< @old{RBIMPL_UNREACHABLE} */ +#define UNREACHABLE_RETURN RBIMPL_UNREACHABLE_RETURN /**< @old{RBIMPL_UNREACHABLE_RETURN} */ + +/* likely */ +#if RBIMPL_HAS_BUILTIN(__builtin_expect) +/** + * Asserts that the given Boolean expression likely holds. + * + * @param x An expression that likely holds. + * + * @note Consider this macro carefully. It has been here since when CPUs were + * like babies, but contemporary processors are beasts. They are + * smarter than mare mortals like us today. Their branch predictions + * highly expectedly outperform your use of this macro. + */ +# define RB_LIKELY(x) (__builtin_expect(!!(x), 1)) + +/** + * Asserts that the given Boolean expression likely doesn't hold. + * + * @param x An expression that likely doesn't hold. + */ +# define RB_UNLIKELY(x) (__builtin_expect(!!(x), 0)) +#else +# define RB_LIKELY(x) (x) +# define RB_UNLIKELY(x) (x) +#endif + +#endif /* RUBY_BACKWARD2_ASSUME_H */ |