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c/6677: GCC 3.1 has a bug in signed char treatment
- From: knu at iDaemons dot org
- To: gcc-gnats at gcc dot gnu dot org
- Date: 16 May 2002 14:32:29 -0000
- Subject: c/6677: GCC 3.1 has a bug in signed char treatment
- Reply-to: knu at iDaemons dot org
>Number: 6677
>Category: c
>Synopsis: GCC 3.1 has a bug in signed char treatment
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: wrong-code
>Submitter-Id: net
>Arrival-Date: Thu May 16 07:36:02 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator: FreeBSD-gnats-submit@freebsd.org
>Release: gcc (GCC) 3.1 [FreeBSD] 20020509 (prerelease)
>Organization:
>Environment:
FreeBSD archon.local.idaemons.org 5.0-CURRENT FreeBSD 5.0-CURRENT #7: Mon May 6 01:19:19 JST 2002 root@archon.local.idaemons.org:/villa/work/obj/freebsd/src/villa/src/sys/ARCHON i386
gcc (GCC) 3.1 [FreeBSD] 20020509 (prerelease)
>Description:
GCC 3.1 has a bug in signed char treatment. See below.
>How-To-Repeat:
knu@archon[2]% cat a.c
int main(void)
{
unsigned char i = 127;
char j;
printf("%d\n", ((char)(i << 1)));
j = ((char)(i << 1)) / 2;
printf("%d\n", j);
j = ((char)(i << 1));
printf("%d\n", j / 2);
return 0;
}
knu@archon[2]% cc a.c
knu@archon[2]% ./a.out
-2
127
-1
The second value should be equal to the third (-1). (char is signed on
the platform)
I can reproduce this with any of -O[0-6].
With gcc 2.95.x, this test code properly results in -2, -1 and -1.
>Fix:
Changing the division from `/ 2' to `>> 1' seems to work around the
problem, but I don't know why.
>Release-Note:
>Audit-Trail:
>Unformatted: