Ruby  3.4.0dev (2024-12-06 revision 892c46283a5ea4179500d951c9d4866c0051f27b)
Macros
assume.h File Reference

(892c46283a5ea4179500d951c9d4866c0051f27b)

Defines ASSUME / RB_LIKELY / UNREACHABLE. More...

#include "ruby/internal/config.h"
#include "ruby/internal/assume.h"
#include "ruby/internal/has/builtin.h"
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Macros

#define ASSUME   RBIMPL_ASSUME
 Old name of RBIMPL_ASSUME. More...
 
#define UNREACHABLE   RBIMPL_UNREACHABLE()
 Old name of RBIMPL_UNREACHABLE. More...
 
#define UNREACHABLE_RETURN   RBIMPL_UNREACHABLE_RETURN
 Old name of RBIMPL_UNREACHABLE_RETURN. More...
 
#define RB_LIKELY(x)   (__builtin_expect(!!(x), 1))
 Asserts that the given Boolean expression likely holds. More...
 
#define RB_UNLIKELY(x)   (__builtin_expect(!!(x), 0))
 Asserts that the given Boolean expression likely doesn't hold. More...
 

Detailed Description

Defines ASSUME / RB_LIKELY / UNREACHABLE.

Author
Ruby developers ruby-.nosp@m.core.nosp@m.@ruby.nosp@m.-lan.nosp@m.g.org
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.

Definition in file assume.h.

Macro Definition Documentation

◆ RB_LIKELY

#define RB_LIKELY (   x)    (__builtin_expect(!!(x), 1))

Asserts that the given Boolean expression likely holds.

Parameters
xAn 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.

Definition at line 43 of file assume.h.

◆ RB_UNLIKELY

#define RB_UNLIKELY (   x)    (__builtin_expect(!!(x), 0))

Asserts that the given Boolean expression likely doesn't hold.

Parameters
xAn expression that likely doesn't hold.

Definition at line 50 of file assume.h.