[Bug c/53332] New: #pragma STDC FLOAT_CONST_DECIMAL64 ON done wrong

[tydeman at tybor dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53332

             Bug #: 53332
           Summary: #pragma STDC FLOAT_CONST_DECIMAL64 ON    done wrong
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: tydeman@tybor.com


The following code shows problems with floating-point constants and implied
decimal suffix.  x10 ends up as a NaN and x2 ends up as zero (both wrong).

#define __STDC_WANT_DEC_FP__    /* Tell implementation that we want Decimal FP
*/

#pragma STDC FLOAT_CONST_DECIMAL64 ON

#include <stdio.h>

int main(void){
  double     d2  = (_Decimal64)((28.DD/3.DD-9.DD) - (31.DD/3.DD-10.DD));    /*
decimal FP */
  _Decimal64 d10 = (_Decimal64)((28.DD/3.DD-9.DD) - (31.DD/3.DD-10.DD));
  double     b2  = (_Decimal64)((28.D /3.D -9.D ) - (31.D /3.D -10.D ));    /*
binary FP */
  _Decimal64 b10 = (_Decimal64)((28.D /3.D -9.D ) - (31.D /3.D -10.D ));
  double     x2  = (_Decimal64)((28./3.-9.) - (31./3.-10.));    /* should be
decimal FP */
  _Decimal64 x10 = (_Decimal64)((28./3.-9.) - (31./3.-10.));
  if( d2 != x2 ){
    (void) printf(" d2 is %g,  b2 is %g,  x2 is %g\n", (double)d2,  (double)b2,
 (double)x2  );
  } 
  if( d10 != x10 ){
    (void) printf("d10 is %g, b10 is %g, x10 is %g\n", (double)d10,
(double)b10, (double)x10 );
  } 

  return 0;
}

This is on Intel CPUs in both 32-bit and 64-bit mode.
This is with Fedora Core Linux 14 thru 17.
This is with gcc 4.5.1 thru 4.7.0