'\" te
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.TH feupdateenv 3M "12 Jul 2006" "SunOS 5.11" "Mathematical Library Functions"
.SH NAME
feupdateenv \- update floating-point environment
.SH SYNOPSIS
.LP
.nf
c99 [ \fIflag\fR... ] \fIfile\fR... \fB-lm\fR [ \fIlibrary\fR... ]
#include <fenv.h>

\fBint\fR \fBfeupdateenv\fR(\fBconst fenv_t *\fR\fIenvp\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The \fBfeupdateenv()\fR function attempts to save the currently raised
floating-point exceptions in its automatic storage, attempts to install the
floating-point environment represented by the object pointed to by \fIenvp\fR,
and then attempts to raise the saved floating-point exceptions. The \fIenvp\fR
argument points to an object set by a call to \fBfegetenv\fR(3M) or
\fBfeholdexcept\fR(3M), or equals a floating-point environment macro.
.SH RETURN VALUES
.sp
.LP
The \fBfeupdateenv()\fR function returns 0 if and only if all the required
actions were successfully carried out.
.SH ERRORS
.sp
.LP
No errors are defined.
.SH EXAMPLES
.sp
.LP
The following example demonstrates sample code to hide spurious underflow
floating-point exceptions:
.LP
\fBExample 1 \fRHide spurious underflow floating-point exceptions.
.sp
.in +2
.nf
#include <fenv.h>
double f(double x)
{
#   pragma STDC FENV_ACCESS ON
    double result;
    fenv_t save_env;
    feholdexcept(&save_env);
    // compute result
    if (/* test spurious underflow */)
    feclearexcept(FE_UNDERFLOW);
    feupdateenv(&save_env);
    return result;
}
.fi
.in -2

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(5) for descriptions of the following attributes:
.sp

.sp
.TS
tab() box;
cw(2.75i) |cw(2.75i) 
lw(2.75i) |lw(2.75i) 
.
ATTRIBUTE TYPEATTRIBUTE VALUE
_
Interface StabilityStandard
_
MT-LevelMT-Safe
.TE

.SH SEE ALSO
.sp
.LP
\fBfegetenv\fR(3M), \fBfeholdexcept\fR(3M), \fBfenv.h\fR(3HEAD),
\fBattributes\fR(5), \fBstandards\fR(5)
.SH NOTES
.sp
.LP
In a multithreaded program, the \fBfeupdateenv()\fR function affects the
floating point environment only for the calling thread.
.sp
.LP
When the \fBFEX_CUSTOM\fR handling mode is in effect for an exception, raising
that exception using \fBfeupdateenv()\fR causes the handling function to be
invoked. The handling function can then modify the exception flags to be set as
described in \fBfex_set_handling\fR(3M).  Any result value the handler supplies
will be ignored.
.sp
.LP
The \fBfeupdateenv()\fR function automatically installs and deinstalls
\fBSIGFPE\fR handlers and sets and clears the trap enable mode bits in the
floating point status register as needed. If a program uses these functions and
attempts to install a \fBSIGFPE\fR handler or control the trap enable mode bits
independently, the resulting behavior is not defined.
.sp
.LP
As described in \fBfex_set_handling\fR(3M), when a handling function installed
in \fBFEX_CUSTOM\fR mode is invoked, all exception traps are disabled (and will
not be reenabled while \fBSIGFPE\fR is blocked). Thus, attempting to change the
environment from within a handler by calling \fBfesetenv\fR(3M) or
\fBfeupdateenv\fR might not produce the expected results.