_control87()

update the control word of the 8087/80287/80387/80486

Synopsis:

#include <float.h>
unsigned int _control87( unsigned int newcw,
                         unsigned int mask );

Description:

The _control87() function updates the control word of the 8087/80287/80387/80486. If mask is zero, then the control word is not updated. If mask is nonzero, then the control word is updated with bits from newcw corresponding to each bit that is on in mask.

Returns:

The new control word. The description of bits defined for the control word is found in the <float.h> header file.

Examples:

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

char *status[2] = { "disabled", "enabled" };

void main()
  {
    unsigned int fp_cw = 0;
    unsigned int fp_mask = 0;
    unsigned int bits;

    fp_cw = _control87( fp_cw,
                        fp_mask );

    printf( "Interrupt Exception Masks\n" );
    bits = fp_cw & MCW_EM;
    printf( "  Invalid Operation exception %s\n",
            status[ (bits & EM_INVALID) == 0 ] );
    printf( "  Denormalized exception %s\n",
            status[ (bits & EM_DENORMAL) == 0 ] );
    printf( "  Divide-By-Zero exception %s\n",
            status[ (bits & EM_ZERODIVIDE) == 0 ] );
    printf( "  Overflow exception %s\n",
            status[ (bits & EM_OVERFLOW) == 0 ] );
    printf( "  Underflow exception %s\n",
            status[ (bits & EM_UNDERFLOW) == 0 ] );
    printf( "  Precision exception %s\n",
            status[ (bits & EM_PRECISION) == 0 ] );

    printf( "Infinity Control = " );
    bits = fp_cw & MCW_IC;
    if( bits == IC_AFFINE )     printf( "affine\n" );
    if( bits == IC_PROJECTIVE ) printf( "projective\n" );

    printf( "Rounding Control = " );
    bits = fp_cw & MCW_RC;
    if( bits == RC_NEAR )       printf( "near\n" );
    if( bits == RC_DOWN )       printf( "down\n" );
    if( bits == RC_UP )         printf( "up\n" );
    if( bits == RC_CHOP )       printf( "chop\n" );

    printf( "Precision Control = " );
    bits = fp_cw & MCW_PC;
    if( bits == PC_24 )         printf( "24 bits\n" );
    if( bits == PC_53 )         printf( "53 bits\n" );
    if( bits == PC_64 )         printf( "64 bits\n" );
  }

Classification:

Intel

See also:

_clear87(), _fpreset(), _status87()