[Bug c/24387] New: int-float cast fails for large int values

[Bug c/24387] New: int-float cast fails for large int values

[neff dot kevin at mayo dot edu]

Seems that there is an error when casting an int to a float, at least for
certain values of the integer.  The first integer to fail is 2^24... Note
also that it's only odd integer values that are a problem.

At least one other version (2.3.2) of gcc did not have this problem.

  -bash-2.05b$ gcc main_cast.c  &&  ./a.out | head
  Size of integers: 4
  Failed: 16777216.000000 != 16777217.000000
  Failed: 16777220.000000 != 16777219.000000
  Failed: 16777220.000000 != 16777221.000000
  Failed: 16777224.000000 != 16777223.000000
  Failed: 16777224.000000 != 16777225.000000
  Failed: 16777228.000000 != 16777227.000000
  Failed: 16777228.000000 != 16777229.000000
  Failed: 16777232.000000 != 16777231.000000
  Failed: 16777232.000000 != 16777233.000000
  -bash-2.05b$


--- main_cast.c ---

#include <stdio.h>
#include <limits.h>


int main()
{
  int i;
  float f;

  printf( "Size of integers: %i\n", sizeof(int) );

  for(  i = 0;  i < INT_MAX;  i += 1  )
  {
    f = (float)i;
    if(  f != ((float)i)  )
      printf( "Failed: %f != %f\n", f, (float)i );
  }

  return 0;
}


-- 
           Summary: int-float cast fails for large int values
           Product: gcc
           Version: 4.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: neff dot kevin at mayo dot edu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24387

[Bug c/24387] int-float cast fails for large int values

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2005-10-15 18:34 -------


*** This bug has been marked as a duplicate of 323 ***


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |DUPLICATE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24387

[Bug c/24387] int-float cast fails for large int values

[neff dot kevin at mayo dot edu]

------- Comment #2 from neff dot kevin at mayo dot edu  2005-10-20 14:01 -------

Oops.  floats only store 23 or 24 bits of mantissa.

I guess it's a feature...


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24387