[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]

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: unassig...@gcc.gnu.org

        ReportedBy: b1262...@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.