NAME

fegetenv, feholdexcept, fesetenv, feupdateenv —

floating-point environment save and restore

LIBRARY

Math Library (libm, -lm)

SYNOPSIS

#include <fenv.h>

#pragma STDC FENV_ACCESS ON

int
fegetenv(fenv_t *envp);

int
feholdexcept(fenv_t *envp);

int
fesetenv(const fenv_t *envp);

int
feupdateenv(const fenv_t *envp);

DESCRIPTION

The floating-point environment includes exception flags and masks, the current rounding mode, and other architecture-specific settings. However, it does not include the floating-point register file.

The fegetenv() function stores the current floating-point environment in the object pointed to by envp, whereas feholdexcept() saves the current environment, then clears all exception flags and masks all floating-point exceptions.

The fesetenv() function restores a previously saved environment. The feupdateenv() function restores a saved environment as well, but it also raises any exceptions that were set in the environment it replaces.

The feholdexcept() function is often used with feupdateenv() or fesetenv() to suppress spurious exceptions that occur as a result of intermediate computations. An example in fenv(3) demonstrates how to do this.

RETURN VALUES

The fegetenv(), feholdexcept(), fesetenv(), and feupdateenv() functions return 0 if they succeed, and non-zero otherwise.

STANDARDS

The fegetenv(), feholdexcept(), fesetenv(), and feupdateenv() functions conform to ISO/IEC 9899:1999 (“ISO C99”).

HISTORY

These routines first appeared in FreeBSD 5.3.