NAME
fesetflushtozero() — set floating-point underflow mode
SYNOPSIS
#include <fenv.h>
void fesetflushtozero(int);
DESCRIPTION
The
fesetflushtozero()
function sets the current underflow mode.
If the argument is 1, the
underflow mode is set to flush-to-zero mode.
If the argument is zero,
the underflow mode is set to IEEE-754-compliant (gradual) underflow
mode.
For arguments other than 1 or zero, the effect is undefined.
The default underflow mode is IEEE-754-compliant.
Flush-to-zero mode, also known as fast underflow mode, is supported on
most PA1.1 systems and on all PA2.0 systems. On HP 9000
systems, most underflow cases are supported by trapping into the
kernel, where the IEEE-mandated conversion of the result into a
denormalized value or zero is accomplished by software emulation.
Flush-to-zero mode causes the hardware to substitute a zero for the
result of an operation, with no fault occurring.
This may be a
significant performance optimization for applications that underflow
frequently.
Flush-to-zero mode also causes denormalized
floating-point operands to be treated as if they were true zero
operands.
To use this function, compile either with the default
-Ae
option or with the
-Aa
and
-D_HPUX_SOURCE
options. Make sure your program includes
<fenv.h>.
Link in the math library by specifying
-lm
on the compiler or linker command line.
For more information, see the
HP-UX Floating-Point Guide.
ERRORS
No errors are defined.
EXAMPLE
Save the current underflow mode, set flush-to-zero mode, and restore
the previous mode.
#include <fenv.h>
/*...*/
int fm_saved;
fm_saved = fegetflushtozero();
fesetflushtozero(1);
/*...*/
fesetflushtozero(fm_saved);
AUTHOR
fesetflushtozero()
was developed by HP and is not required by any current standard.
