https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125817
Bug ID: 125817
Summary: __builtin_popcountg() doesn't work for large _BitInt()
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: [email protected]
Target Milestone: ---
>From the program below, __builtin_popcountg() only counts the low 32 bits of a
_BitInt(256). Is there any limit in how large a bitint can be as input to this
builtin? If so, I'd expect a diagnostic when passing a larger one. If not
(most likely), then this seems to be just an implementation bug.
alx@devuan:~/tmp$ cat foo.c
#include <stdcountof.h>
#include <stddef.h>
#include <stdio.h>
#include <string.h>
union ln {
unsigned _BitInt(256) ln;
unsigned _BitInt(1) e[256];
};
[[gnu::noipa]]
void
print_ln(FILE *stream, size_t n, const union ln l[1])
{
char *p;
char txt[n + countof("\n")];
p = txt;
for (size_t i = 0; i < n; i++)
*p++ = l->e[i] + '0';
strcpy(p, "\n");
fputs(txt, stream);
}
[[gnu::noipa]]
size_t
sum_ln(const union ln l[1])
{
return __builtin_popcountg(l->ln);
}
int
main(void)
{
union ln l = {};
l.e[5] = true;
l.e[4] = true;
l.e[2] = true;
l.e[7] = true;
l.e[20] = true;
l.e[30] = true;
l.e[60] = true;
l.e[77] = true;
printf("%zu\n", sum_ln(&l));
print_ln(stdout, 128, &l);
}
alx@devuan:~/tmp$ gcc-16 -Wall -Wextra foo.c
alx@devuan:~/tmp$ ./a.out
6
00101101000000000000100000000010000000000000000000000000000010000000000000000100000000000000000000000000000000000000000000000000
alx@devuan:~/tmp$ ./a.out | tail -n1 | tr -d 0 | wc -L
8
