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_clear87, _clearfp

  • Άρθρο

Gets and clears the floating-point status word.

Syntax

unsigned int _clear87( void );
unsigned int _clearfp( void );

Return value

The bits in the value returned indicate the floating-point status before the call to _clear87 or _clearfp. For a complete definition of the bits returned by _clear87, see Float.h. Many of the math library functions modify the 8087/80287 status word, with unpredictable results. Return values from _clear87 and _status87 become more reliable as fewer floating-point operations are performed between known states of the floating-point status word.

Remarks

The _clear87 function clears the exception flags in the floating-point status word, sets the busy bit to 0, and returns the status word. The floating-point status word is a combination of the 8087/80287 status word and other conditions detected by the 8087/80287 exception handler, such as floating-point stack overflow and underflow.

_clearfp is a platform-independent, portable version of the _clear87 routine. It's identical to _clear87 on Intel (x86) platforms and is also supported by the x64 and ARM platforms. To ensure that your floating-point code is portable to x64 and ARM, use _clearfp. If you're only targeting x86 platforms, you can use either _clear87 or _clearfp.

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

Requirements

Routine Required header
_clear87 <float.h>
_clearfp <float.h>

For more compatibility information, see Compatibility.

Example

// crt_clear87.c
// compile with: /Od

// This program creates various floating-point
// problems, then uses _clear87 to report on these problems.
// Compile this program with Optimizations disabled (/Od).
// Otherwise the optimizer will remove the code associated with
// 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", _clear87()  );

   // Store into y is inexact and underflows:
   y = a;
   printf( "Status: %.4x - inexact, underflow\n", _clear87() );

   // y is denormal:
   b = y;
   printf( "Status: %.4x - denormal\n", _clear87() );
}

Status: 0000 - clear
Status: 0003 - inexact, underflow
Status: 80000 - denormal

See also

Math and floating-point support
_control87, _controlfp, __control87_2
_status87, _statusfp, _statusfp2