Re: c/6607: Inconsisitency using right shift operator (signed vs. unsigned shift)

Re: c/6607: Inconsisitency using right shift operator (signed vs. unsigned shift)

[neil]

Synopsis: Inconsisitency using right shift operator (signed vs. unsigned shift)

State-Changed-From-To: open->feedback
State-Changed-By: neil
State-Changed-When: Wed May  8 10:38:30 2002
State-Changed-Why:
    Can you reproduce this behaviour for a shift of less than 32 bits?
    A shift of the same number of bits as the width of the
    type gives undefined behaviour, so the testcase you post
    is not a bug as-is.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=6607

Re: c/6607: Inconsisitency using right shift operator (signed vs. unsigned shift)

[neil]

Synopsis: Inconsisitency using right shift operator (signed vs. unsigned shift)

State-Changed-From-To: feedback->closed
State-Changed-By: neil
State-Changed-When: Thu May  9 23:04:06 2002
State-Changed-Why:
    Not a bug.  This is undefined behaviour.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=6607

c/6607: Inconsisitency using right shift operator (signed vs. unsigned shift)

[wheisler]

>Number:         6607
>Category:       c
>Synopsis:       Inconsisitency using right shift operator (signed vs. unsigned shift)
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed May 08 10:16:01 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     Bill Heisler
>Release:        gcc 2.96 20000731
>Organization:
>Environment:
RH 7.1 Intel Glibc 2.2.3-16 gcc 2.96
>Description:
When using a right shift operator that can be calculated at compile time, the operator performs an unsigned shift (prepends zeros).  If the shift is parameterized, and is calculated at run time, a signed shift is performed (prepends high order bit).
>How-To-Repeat:
#include <stdio.h>

int main (int argc, char ** argv) {
   unsigned int i = 0xffffffff >> 32;
   unsigned int j = 0xffffffff;

   j = j >> 32;

   printf("i -- %x\nj -- %x\n", i, j);
}
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: