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COPROC.C
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─────Run-Time Library───────────────────────────────────────────────────────
/* COPROC.C illustrates use of the status and control words of a floating-
* point coprocessor (or emulator). Functions illustrated include:
* _clear87 _status87 _control87
*/
#include <stdio.h>
#include <conio.h>
#include <float.h>
#include <stdlib.h>
#include <string.h>
double dx = 1e-40, dy;
float fx, fy;
unsigned status, control;
char tmpstr[20];
char *binstr( int num, char *buffer );
void main()
{
printf( "Status Word Key:\n" );
printf( "B\tBusy flag\n0-3\tCondition codes\nS\tStack top pointer\n" );
printf( "E\tError summary\nF\tStack flag\nP\tPrecision exception\n" );
printf( "U\tUnderflow exception\nO\tOverflow exception\n" );
printf( "Z\tZero divide exception\nD\tDenormalized exception\n" );
printf( "I\tInvalid operation exception\n\n" );
binstr( _clear87(), tmpstr );
printf( "B3SSS210EFPUOZDI Function\tCondition\n\n" );
printf( "%16s _clear87\tAfter clearing\n", tmpstr );
/* Storing double to float that hasn't enough precision for it
* causes underflow and precision exceptions.
*/
fx = dx;
binstr( _status87(), tmpstr );
printf( "%16s _status87\tAfter moving double to float\n", tmpstr );
/* Storing float with lost precision back to double adds denormalized
* exception (previous exceptions remain).
*/
dy = fx;
binstr( _clear87(), tmpstr );
printf( "%16s _clear87\tAfter moving float to double\n", tmpstr );
/* Using _clear87() erases previous exceptions. */
fy = dy;
binstr( _status87(), tmpstr );
printf( "%16s _status87\tAfter moving double to float\n\n", tmpstr );
_getch();
printf( "Control Word Key:\n" );
printf( "i\tInfinity control\nr\tRounding control\n" );
printf( "p\tPrecision control\ne\tInterrupt enable mask\n" );
printf( "U\tUnderflow mask\nO\tOverflow mask\n" );
printf( "Z\tZero divide mask\nD\tDenormalized mask\n" );
printf( "I\tInvalid operation mask\n\n" );
printf( "???irrppe?PUOZDI Result\n" );
fy = .1;
/* Show current control word. */
binstr( _control87( 0, 0 ), tmpstr );
printf( "%16s %.1f * %.1f = %.15e with initial precision\n",
tmpstr, fy, fy, fy * fy );
/* Set precision to 24 bits. */
binstr( _control87( _PC_24, _MCW_PC ), tmpstr );
printf( "%16s %.1f * %.1f = %.15e with 24-bit precision\n",
tmpstr, fy, fy, fy * fy );
/* Restore default. */
binstr( _control87( _CW_DEFAULT, 0xffff ), tmpstr );
printf( "%16s %.1f * %.1f = %.15e with default precision\n",
tmpstr, fy, fy, fy * fy );
}
/* Converts integer to string of 16 binary characters. */
char *binstr( int num, char *buffer )
{
char tmp[17];
int len;
memset( buffer, '0', 16 );
len = strlen( _itoa( num, tmp, 2 ) );
strcpy( buffer + 16 - len, tmp );
return buffer;
}
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