_status87, _statusfp

Get the floating point status word.

unsigned int _status87( void );

unsigned int _statusfp( void );

For additional compatibility information, see Compatibility in the Introduction.

Libraries

Return Value

The bits in the value returned indicate the floating-point status. See the FLOAT.H include file for a complete definition of the bits returned by _status87.

Many math library functions modify the 8087/80287 status word, with unpredictable results. Return values from _clear87 and _status87 are more reliable if fewer floating-point operations are performed between known states of the floating-point status word.

Remarks

The _status87 function gets the floating-point status word. The status word is a combination of the 8087/80287/80387 status word and other conditions detected by the 8087/80287/80387 exception handler, such as floating-point stack overflow and underflow. Unmasked exceptions are checked for before returning the contents of the status word. This means that the caller is informed of pending exceptions.

_statusfp is a platform-independent, portable version of _status87. It is identical to _status87 on Intel (x86) platforms and is also supported by the MIPS platform. To ensure that your floating-point code is portable to MIPS, use _statusfp. If you are only targeting x86 platforms, use either _status87 or _statusfp.

Example

/* STATUS87.C: This program creates various floating-point errors and
 * then uses _status87 to display messages indicating these problems.
 * Compile this program with optimizations disabled (/Od). Otherwise,
 * the optimizer removes the code related to the unused floating-
 * point values.
 */

#include <stdio.h>
#include <float.h>

void main( void )
{
   double a = 1e-40, b;
   float  x, y;

   printf( "Status = %.4x - clear\n",_status87() );

   /* Assignment into y is inexact & underflows: */
   y = a;
   printf( "Status = %.4x - inexact, underflow\n", _status87() );

   /* y is denormal: */
   b = y;
   printf( "Status = %.4x - inexact underflow, denormal\n", 
           _status87() );

   /* Clear user 8087: */
   _clear87();
}

Output

Status = 0000 - clear
Status = 0003 - inexact, underflow
Status = 80003 - inexact underflow, denormal

Floating-Point Support Routines

See Also   _clear87, _control87