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* [Bug c/35774] New: wrong code on casting int result to signed char
@ 2008-03-31 14:34 hongbo dot yang at mathworks dot com
2008-03-31 16:10 ` [Bug c/35774] " rguenth at gcc dot gnu dot org
0 siblings, 1 reply; 2+ messages in thread
From: hongbo dot yang at mathworks dot com @ 2008-03-31 14:34 UTC (permalink / raw)
To: gcc-bugs
In the main function there is a cast casting int result to signed char.
typedef int int32_T;
typedef unsigned int uint32_T;
typedef signed char int8_T;
#include <stdio.h>
int main(void)
{
int32_T i;
uint32_T numerator;
for (i = 126; i < 256; i++) {
numerator = (uint32_T)((int8_T)(-128 + i) + 128) * 63U;
fprintf(stdout, "i = %d numerator = %u\n", i, numerator);
}
return numerator;
}
This program is compiled with gcc -O0 -g,
I suppose the result of the variable "numerator" should be:
126 * 63
127 * 63
128 * 63
....
But the printed result is equal to:
126 * 63
127 * 63
- 128 * 63
....
The generated assembly code on mac with Intel Core-2-Duo processor is:
movl -24(%ebp), %eax
movsbl %al,%edx
movl %edx, %eax
sall $6, %eax
subl %edx, %eax
movl %eax, -20(%ebp)
It seems both -128 and +128 are ignored.
This problem doesn't appear on gcc 4.1.1.
--
Summary: wrong code on casting int result to signed char
Product: gcc
Version: 4.0.1
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: hongbo dot yang at mathworks dot com
GCC build triplet: i686-linux-gnu
GCC host triplet: i686-linux-gnu
GCC target triplet: i686-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35774
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug c/35774] wrong code on casting int result to signed char
2008-03-31 14:34 [Bug c/35774] New: wrong code on casting int result to signed char hongbo dot yang at mathworks dot com
@ 2008-03-31 16:10 ` rguenth at gcc dot gnu dot org
0 siblings, 0 replies; 2+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2008-03-31 16:10 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from rguenth at gcc dot gnu dot org 2008-03-31 16:10 -------
GCC 4.0 is no longer maintained. Fixed in 4.1.0.
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Keywords| |wrong-code
Known to fail| |4.0.4
Resolution| |FIXED
Target Milestone|--- |4.1.0
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35774
^ permalink raw reply [flat|nested] 2+ messages in thread
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2008-03-31 14:34 [Bug c/35774] New: wrong code on casting int result to signed char hongbo dot yang at mathworks dot com
2008-03-31 16:10 ` [Bug c/35774] " rguenth at gcc dot gnu dot org
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