_status87, _statusfp, _statusfp2

Article
11/16/2012

Get the floating point status word.

unsigned int _status87( void );
unsigned int _statusfp( void );
void _statusfp2(unsigned int *px86, unsigned int *pSSE2)

Parameters

px86
This address is filled with the status word for the x87 floating point unit.
pSSE2
This address is filled with the status word for the SSE2 floating point unit.

Return Value

For _status87 and _statusfp, 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. _statusfp2 has no return value.

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.

_statusfp2 is recommended for chips (such as the Pentium IV and later) that have both an x87 and an SSE2 floating point processor. For _statusfp2, the addresses are filled in with the floating-point status word for both the x87 or the SSE2 floating-point processor. When using a chip that supports x87 and SSE2 floating point processors, EM_AMBIGUOUS is set to 1 if _statusfp or _controlfp is used and the action was ambiguous because it could refer to the x87 or the SSE2 floating-point status word.

These functions are deprecated when compiling with /clr (Common Language Runtime Compilation) or /clr:pure because the common language runtime only supports the default floating-point precision.

Requirements

Routine	Required header
_status87, _statusfp, _statusfp2	<float.h>

For additional compatibility information, see Compatibility in the Introduction.

Example

// crt_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>

int 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();
}

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

.NET Framework Equivalent

Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.

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