[Bug c/55967] New: rightshift an unsigned value (X) by it's number of bits does not always yield 0, when X is an unsigned that's leftshifted by it's number of bits and offset

["b1262178 at rmqkr dot net" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55967

             Bug #: 55967
           Summary: rightshift an unsigned value (X) by it's number of
                    bits does not always yield 0, when X is an unsigned
                    that's leftshifted by it's number of bits and offset
    Classification: Unclassified
           Product: gcc
           Version: 4.6.2
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: b1262178@rmqkr.net


Hi,

I'm curring gcc via MinGW on a 32 bit PC:

The output of the following 

/********************************************/
#include <stdio.h>

int main(void)
{
  printf("%lu\n",  ((1U<<(32))));
  printf("%lu\n",  ((1U<<(32))) + 0x80000000U);

  printf("%lu\n", (((1U<<(32))) + 0x80000000U) >> 32U); /* expecting 0 but get
0x80000000U instead. BUG???? */
  printf("%lu\n", (               0x80000000U) >> 32U); /* compare: here
correctly get 0! */
  printf("%lu\n", (((1U<<(32)))              ) >> 32U); /* compare: here
correctly get 0! */
  return 0;

  return 0;
}
/********************************************/

is:

0
2147483648
2147483648 // Bug!
0
0

THE 3rd output line IS A BUG, right? I expect to get 0.
And why do I expect 0. Because I've got a 32-bit number and rightshift it by
32.

Ouput lines 4 and 5 do that correctly: they yield 0.

So what's going on in line 3 ?






gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=c:/mingw/bin/../libexec/gcc/mingw32/4.6.2/lto-wrapper.exe
Target: mingw32
Configured with: ../gcc-4.6.2/configure
--enable-languages=c,c++,ada,fortran,objc,obj-c++ --disable-sjlj-exceptions
--with-dwarf2 --enable-shared --enable-libgomp --disable-win32-registry
--enable-libstdcxx-debug --enable-version-specific-runtime-libs --build=mingw32
--prefix=/mingw
Thread model: win32
gcc version 4.6.2 (GCC)


Thanks.