[Bug c/47146] New: Floating point to integer conversions

[babelart at yahoo dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47146

           Summary: Floating point to integer conversions
           Product: gcc
           Version: 4.3.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: babelart@yahoo.com


#include <stdio.h>
#include <stdlib.h>

//-----------------------------------------------------------------------------
int32_t main(int argc, char **argv)
//-----------------------------------------------------------------------------
{
    float elapsed = 0.3894949;

    fprintf( stdout, "Float 0.3894949=%f\n", elapsed );
    fprintf( stdout, "Float 0.3894949 * 100.0=%f\n", elapsed * 100.0 );
    fprintf( stdout, "Integer Cast 0.3894949 * 100.0=%d\n", (int32_t) (elapsed
* 100.0) );

    elapsed = 0.3894949 * 100;
    int32_t ielapsed = 0.3894949 * 100;

    fprintf( stdout, "Float=%f\n", elapsed );
    fprintf( stdout, "Integer=%d\n", ielapsed );

    fprintf( stdout, "------------------------------\n" );
    elapsed = 0.39;

    fprintf( stdout, "Float 0.39=%f\n", elapsed );
    fprintf( stdout, "Float 0.39 * 100.0=%f\n", elapsed * 100.0 );
    fprintf( stdout, "Integer Cast 0.39 * 100.0=%d\n", (int32_t) (elapsed *
100.0) );

    elapsed = 0.39 * 100;
    ielapsed = 0.39 * 100;

    fprintf( stdout, "Float=%f\n", elapsed );
    fprintf( stdout, "Integer=%d\n", ielapsed );

    exit( 0 );
}


The above code generates the following:

Float 0.3894949=0.389495
Float 0.3894949 * 100.0=38.949490
Integer Cast 0.3894949 * 100.0=38
Float=38.949490
Integer=38
------------------------------
Float 0.39=0.390000
Float 0.39 * 100.0=38.999999
Integer Cast 0.39 * 100.0=38
Float=39.000000
Integer=39

Casting and rounding seems to be a problem.

The compiler build options are:

Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.3.4-6'
--with-bugurl=file:///usr/share/doc/gcc-4.3/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared
--enable-multiarch --enable-linker-build-id --with-system-zlib
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--enable-nls --with-gxx-include-dir=/usr/include/c++/4.3 --program-suffix=-4.3
--enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --enable-mpfr
--enable-targets=all --with-tune=generic --enable-checking=release
--build=i486-linux-gnu --host=i486-linux-gnu --target=i486-linux-gnu
Thread model: posix
gcc version 4.3.4 (Debian 4.3.4-6) 


The system is;

Linux devel 2.6.30-2-686 #1 SMP Sat Sep 26 01:16:22 UTC 2009 i686 GNU/Linux

The processor is:

processor    : 0
vendor_id    : AuthenticAMD
cpu family    : 15
model        : 107
model name    : AMD Athlon(tm) 64 X2 Dual Core Processor 5200+
stepping    : 2
cpu MHz        : 2712.740
cache size    : 512 KB