Also, fix a case where an uninitialized value could be used, potentially resulting in errors not being reported (although I haven’t seen that in practice).
This fixes problems where >>= operations might not use an arithmetic shift in certain cases where they should, as in the below program:
#include <stdio.h>
int main (void)
{
int i;
unsigned u;
long l;
unsigned long ul;
i = -1;
u = 1;
i >>= u;
printf("%i\n", i); /* should be -1 */
l = -1;
ul = 3;
l >>= ul;
printf("%li\n", l); /* should be -1 */
}
This is necessary so that subsequent processing sees the correct expression type and proceeds accordingly. In particular, without this patch, the casts in the below program were erroneously ignored:
#include <stdio.h>
int main(void)
{
unsigned int u;
unsigned char c;
c = 0;
u = (unsigned char)~c;
printf("%u\n", u);
c = 200;
printf("%i\n", (unsigned char)(c+c));
}
This is as required by the C standards: the type of the right operand should not affect the result type.
The following program demonstrates problems with the old behavior:
#include <stdio.h>
int main(void)
{
unsigned long ul;
long l;
unsigned u;
int i;
ul = 0x8000 << 1L; /* should be 0 */
printf("%lx\n", ul);
l = -1 >> 1U; /* should be -1 */
printf("%ld\n", l);
u = 0xFF10;
l = 8;
ul = u << l; /* should be 0x1000 */
printf("%lx\n", ul);
l = -4;
ul = 1;
l = l >> ul; /* should be -2 */
printf("%ld\n", l);
}
The following demonstrates cases that would erroneously be allowed (and misleadingly give a size of 0) before:
#include <stdio.h>
struct s *S;
int main(void)
{
printf("%lu %lu\n", sizeof(struct s), sizeof *S);
}
The following test case demonstrates the problem:
#include <stdio.h>
int main (void)
{
if (sizeof(int) - 5 < 0) puts("error 1");
if (sizeof &main - 9 < 0) puts("error 2");
}
This affected binary or unary expressions with constant operands, at least one of which was of type unsigned long.
The following test case demonstrates the problem:
#include <stdio.h>
int main (void)
{
if (0 + 0x80000000ul < 0) puts("error 1");
if (~0ul < 0) puts("error 2");
}
These would previously be allowed, with the void value treated as if it was unsigned long.
Void values are still allowed for the second and third operands of the ?: operator, but only if they are both void. This is as required by the C standard.
Unsigned constants in the range 0x8000-0xFFFF were erroneously being treated like negative signed values in some contexts, including in array declarators and in the case labels of switch statements where the expression switched over has type long or unsigned long.
This could lead to bogus compile errors for array declarations and typedefs such as the following:
typedef char foo[0x8000];
It could also lead to cases in switch statements not being properly matched, as in the following program:
#include <stdio.h>
int main(void)
{
long i = 0xFF00;
switch (i) {
case 0xFF00:
puts("good");
break;
default:
puts("bad");
}
}
Stephen Heumann
mikew50