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From: "z.hegedus@t-systems.com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c/66213] New: unsigned char value range can be greater than sizeof unsigned char Date: Wed, 20 May 2015 10:39:00 -0000 [thread overview] Message-ID: <bug-66213-4@http.gcc.gnu.org/bugzilla/> (raw) 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.hegedus@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.
next reply other threads:[~2015-05-20 10:39 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2015-05-20 10:39 z.hegedus@t-systems.com [this message] 2015-05-20 10:52 ` [Bug c/66213] " mpolacek at gcc dot gnu.org 2015-05-20 11:23 ` z.hegedus@t-systems.com
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