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[Bug c/38341] Wrong warning comparison of promoted ~unsigned with unsigned
- From: "fredrik dot hederstierna at securitas-direct dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 1 Dec 2008 12:55:13 -0000
- Subject: [Bug c/38341] Wrong warning comparison of promoted ~unsigned with unsigned
- References: <bug-38341-17021@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #4 from fredrik dot hederstierna at securitas-direct dot com 2008-12-01 12:55 -------
Heres another example, then I do not think the warnings are due to
optimization.
I have same warnings with both -O0 and -O3.
#include <stdio.h>
typedef unsigned char u8_t;
void test_cast(unsigned char c1, unsigned char c2, u8_t u1, u8_t u2)
{
if (c1 == (unsigned char)(~c2)) {
printf("No warning");
}
if (c1 == ~c2) {
printf("This gives warning");
}
if (u1 == (u8_t)(~u2)) {
printf("This gives warning");
}
if ((unsigned char)u1 == (unsigned char)(~u2)) {
printf("This gives warning");
}
}
The original code that caused this warnings are the TCP/IP stack lwIP, then I
constructed this minimal example.
Original code from lwIP TCP/IP stack:
-------------------------------------
static u8_t ip_reassbitmap[IP_REASS_BUFSIZE / (8 * 8) + 1];
static const u8_t bitmap_bits[8] = { 0xff, 0x7f, 0x3f, 0x1f, 0x0f, 0x07, 0x03,
0x01 };
/.../
if (ip_reassbitmap[ip_reasslen / (8 * 8)] !=
(u8_t) ~ bitmap_bits[ip_reasslen / 8 & 7]) {
/.../
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38341