https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66213
Bug ID: 66213
Summary: unsigned char value range can be greater than sizeof
unsigned char
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: z.hege...@t-systems.com
Target Milestone: ---
Unsigned char can be greater than 1 byte (== sizeof(unsigned char))
Example:
#include <stdio.h>
int main() {
unsigned char a=200, b=80;
int z = a+b;
printf("z=: %d\n", z);
return 0;
}
When data type char or signed char is used in the example above a char overflow
occurs (as expected) but if unsigned char is used the return value can be
greater than 1 byte (or sizeof(unsigned char))
Reason:
Breakpoint 8, 0x004011f6 in main () at char.c:8
(gdb) i r
eax 0x50 80
edx 0xc8 200
Breakpoint 10, 0x00401215 in main () at char.c:10
0x0040121a 10 z = c+d;
(gdb) ni
(gdb) i r
eax 0x50 80
edx 0xffffffc8 -56
Where "c" and "d" are signed chars.
When unsigned char is used gcc uses movzx instead of movsx and probably the
sign bit is overwritten.
