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glibc/math/fenv.h
Joseph Myers e535fb910c Define C23 header version macros 
C23 defines library macros __STDC_VERSION_<header>_H__ to indicate
that a header has support for new / changed features from C23.  Now
that all the required library features are implemented in glibc,
define these macros.  I'm not sure this is sufficiently much of a
user-visible feature to be worth a mention in NEWS.

Tested for x86_64.

There are various optional C23 features we don't yet have, of which I
might look at the Annex H ones (floating-point encoding conversion
functions and _Float16 functions) next.

* Optional time bases TIME_MONOTONIC, TIME_ACTIVE, TIME_THREAD_ACTIVE.
  See
  <https://sourceware.org/pipermail/libc-alpha/2023-June/149264.html>
  - we need to review / update that patch.  (I think patch 2/2,
  inventing new names for all the nonstandard CLOCK_* supported by the
  Linux kernel, is rather more dubious.)

* Updating conform/ tests for C23.

* Defining the rounding mode macro FE_TONEARESTFROMZERO for RISC-V (as
  far as I know, the only architecture supported by glibc that has
  hardware support for this rounding mode for binary floating point)
  and supporting it throughout glibc and its tests (especially the
  string/numeric conversions in both directions that explicitly handle
  each possible rounding mode, and various tests that do likewise).

* Annex H floating-point encoding conversion functions.  (It's not
  entirely clear which are optional even given support for Annex H;
  there's some wording applied inconsistently about only being
  required when non-arithmetic interchange formats are supported; see
  the comments I raised on the WG14 reflector on 23 Oct 2025.)

* _Float16 functions (and other header and testcase support for this
  type).

* Decimal floating-point support.

* Fully supporting __int128 and unsigned __int128 as integer types
  wider than intmax_t, as permitted by C23.  Would need doing in
  coordination with GCC, see GCC bug 113887 for more discussion of
  what's involved.
2025-11-27 19:32:49 +00:00

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/* Copyright (C) 1997-2025 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
/*
* ISO C99 7.6: Floating-point environment <fenv.h>
*/
#ifndef _FENV_H
#define _FENV_H 1
#define __GLIBC_INTERNAL_STARTING_HEADER_IMPLEMENTATION
#include <bits/libc-header-start.h>
/* Get the architecture dependent definitions. The following definitions
are expected to be done:
fenv_t type for object representing an entire floating-point
environment
FE_DFL_ENV macro of type pointer to fenv_t to be used as the argument
to functions taking an argument of type fenv_t; in this
case the default environment will be used
fexcept_t type for object representing the floating-point exception
flags including status associated with the flags
femode_t type for object representing floating-point control modes
FE_DFL_MODE macro of type pointer to const femode_t to be used as the
argument to fesetmode; in this case the default control
modes will be used
The following macros are defined iff the implementation supports this
kind of exception.
FE_INEXACT inexact result
FE_DIVBYZERO division by zero
FE_UNDERFLOW result not representable due to underflow
FE_OVERFLOW result not representable due to overflow
FE_INVALID invalid operation
FE_ALL_EXCEPT bitwise OR of all supported exceptions
The next macros are defined iff the appropriate rounding mode is
supported by the implementation.
FE_TONEAREST round to nearest
FE_UPWARD round toward +Inf
FE_DOWNWARD round toward -Inf
FE_TOWARDZERO round toward 0
*/
#include <bits/fenv.h>
__BEGIN_DECLS
#if __GLIBC_USE (ISOC23)
# define __STDC_VERSION_FENV_H__ 202311L
#endif
/* Floating-point exception handling. */
/* Clear the supported exceptions represented by EXCEPTS. */
extern int feclearexcept (int __excepts) __THROW;
/* Store implementation-defined representation of the exception flags
indicated by EXCEPTS in the object pointed to by FLAGP. */
extern int fegetexceptflag (fexcept_t *__flagp, int __excepts) __THROW;
/* Raise the supported exceptions represented by EXCEPTS. */
extern int feraiseexcept (int __excepts) __THROW;
#if __GLIBC_USE (IEC_60559_BFP_EXT_C23)
/* Set the supported exception flags represented by EXCEPTS, without
causing enabled traps to be taken. */
extern int fesetexcept (int __excepts) __THROW;
#endif
/* Set complete status for exceptions indicated by EXCEPTS according to
the representation in the object pointed to by FLAGP. */
extern int fesetexceptflag (const fexcept_t *__flagp, int __excepts) __THROW;
/* Determine which of subset of the exceptions specified by EXCEPTS are
currently set. */
extern int fetestexcept (int __excepts) __THROW;
#if __GLIBC_USE (IEC_60559_BFP_EXT_C23)
/* Determine which of subset of the exceptions specified by EXCEPTS
are set in *FLAGP. */
extern int fetestexceptflag (const fexcept_t *__flagp, int __excepts) __THROW;
#endif
/* Rounding control. */
/* Get current rounding direction. */
extern int fegetround (void) __THROW __attribute_pure__;
/* Establish the rounding direction represented by ROUND. */
extern int fesetround (int __rounding_direction) __THROW;
/* Floating-point environment. */
/* Store the current floating-point environment in the object pointed
to by ENVP. */
extern int fegetenv (fenv_t *__envp) __THROW;
/* Save the current environment in the object pointed to by ENVP, clear
exception flags and install a non-stop mode (if available) for all
exceptions. */
extern int feholdexcept (fenv_t *__envp) __THROW;
/* Establish the floating-point environment represented by the object
pointed to by ENVP. */
extern int fesetenv (const fenv_t *__envp) __THROW;
/* Save current exceptions in temporary storage, install environment
represented by object pointed to by ENVP and raise exceptions
according to saved exceptions. */
extern int feupdateenv (const fenv_t *__envp) __THROW;
/* Control modes. */
#if __GLIBC_USE (IEC_60559_BFP_EXT_C23)
/* Store the current floating-point control modes in the object
pointed to by MODEP. */
extern int fegetmode (femode_t *__modep) __THROW;
/* Establish the floating-point control modes represented by the
object pointed to by MODEP. */
extern int fesetmode (const femode_t *__modep) __THROW;
#endif
/* NaN support. */
#if (__GLIBC_USE (IEC_60559_BFP_EXT_C23) \
&& defined FE_INVALID \
&& defined __SUPPORT_SNAN__)
# define FE_SNANS_ALWAYS_SIGNAL 1
#endif
#ifdef __USE_GNU
/* Enable individual exceptions. Will not enable more exceptions than
EXCEPTS specifies. Returns the previous enabled exceptions if all
exceptions are successfully set, otherwise returns -1. */
extern int feenableexcept (int __excepts) __THROW;
/* Disable individual exceptions. Will not disable more exceptions than
EXCEPTS specifies. Returns the previous enabled exceptions if all
exceptions are successfully disabled, otherwise returns -1. */
extern int fedisableexcept (int __excepts) __THROW;
/* Return enabled exceptions. */
extern int fegetexcept (void) __THROW;
#endif
__END_DECLS
#endif /* fenv.h */
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