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Add __constfunc and explain how it differs from __pure.

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This commit is contained in:
joerg 2009-07-20 17:46:04 +00:00
parent 71cfba1556
commit 55df17bdb2
1 changed files with 20 additions and 1 deletions
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21
sys/sys/cdefs.h
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@ -1,4 +1,4 @@
/* $NetBSD: cdefs.h,v 1.75 2009/05/12 13:41:44 reinoud Exp $ */
/* $NetBSD: cdefs.h,v 1.76 2009/07/20 17:46:04 joerg Exp $ */
/*
* Copyright (c) 1991, 1993
@ -170,6 +170,19 @@
* GCC2 uses a new, peculiar __attribute__((attrs)) style. All of
* these work for GNU C++ (modulo a slight glitch in the C++ grammar
* in the distribution version of 2.5.5).
*
* GCC defines a pure function as depending only on its arguments and
* global variables. Typical examples are strlen and sqrt.
*
* GCC defines a const function as depending only on its arguments.
* Therefore calling a const function again with identical arguments
* will always produce the same result.
*
* Rounding modes for floating point operations are considered global
* variables and prevent sqrt from being a const function.
*
* Calls to const functions can be optimised away and moved around
* without limitations.
*/
#if !__GNUC_PREREQ__(2, 0)
#define __attribute__(x)
@ -191,6 +204,12 @@
#define __pure
#endif
#if __GNUC_PREREQ__(2, 5)
#define __constfunc __attribute__((__const__))
#else
#define __constfunc
#endif
#if __GNUC_PREREQ__(3, 0)
#define __noinline __attribute__((__noinline__))
#else