[Bug c/26927] New: math function log2 bug

["bxin33 at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

Most likely this bug was reported before; but I couldn't seem to find it in
this database. So, just in case.  The bug is with gcc 3.3.5; I know 3.4.4 works
fine.

=========== test

#include <stdio.h>
#include <math.h>

int main() {
        int g_size = 8;
        int dim;
        double dd;

        dd = log2(g_size);
        dim = (pow(2, (int)dd) >= g_size)?(int)dd : (int)dd + 1;

        printf("log2(%d) = %.1f pow(2, (int)%d) >= %d = %d\n", g_size, dd,
(int)dd, g_size, (pow(2, (int)dd) >= g_size));

        return 0;
}

============ compile & run

> gcc -v
Reading specs from /usr/lib/gcc-lib/i686-pc-linux-gnu/3.3.5/specs
Configured with:
/scratch/portage/tmp/portage/gcc-3.3.5-r1/work/gcc-3.3.5/configure
--enable-version-specific-runtime-libs --prefix=/usr
--bindir=/usr/i686-pc-linux-gnu/gcc-bin/3.3.5
--includedir=/usr/lib/gcc-lib/i686-pc-linux-gnu/3.3.5/include
--datadir=/usr/share/gcc-data/i686-pc-linux-gnu/3.3.5
--mandir=/usr/share/gcc-data/i686-pc-linux-gnu/3.3.5/man
--infodir=/usr/share/gcc-data/i686-pc-linux-gnu/3.3.5/info
--with-gxx-include-dir=/usr/lib/gcc-lib/i686-pc-linux-gnu/3.3.5/include/g++-v3
--host=i686-pc-linux-gnu --disable-altivec --disable-nls --enable-__cxa_atexit
--enable-clocale=gnu --with-system-zlib --disable-checking --disable-werror
--disable-libunwind-exceptions --enable-shared --enable-threads=posix
--enable-java-awt=gtk --enable-languages=c,c++,f77,java
Thread model: posix
gcc version 3.3.5  (Gentoo Linux 3.3.5-r1, ssp-3.3.2-3, pie-8.7.7.1)

> gcc -lm test_math.c
> ./a.out
log2(8) = 1075199136.0 pow(2, (int)1075199136) >= 8 = 1


-- 
           Summary: math function log2 bug
           Product: gcc
           Version: 3.3.5
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bxin33 at gmail dot com
 GCC build triplet: PIII + Gentoo Linux 2.6.11 + GCC 3.3.5
  GCC host triplet: PIII + Gentoo Linux 2.6.11 + GCC 3.3.5
GCC target triplet: PIII + Gentoo Linux 2.6.11 + GCC 3.3.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26927