_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 non-zero, then the control word is updated with bits from newcw corresponding to each bit that is on in mask.

Returns:

The _control87() function returns the new control word. The description of bits defined for the control word is found in the float.h header file.

See also:

_clear87(), _fpreset(), _status87()

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

Systems:

Math