FreeBSD/dummy/popcount.c

#include <stdio.h>
#include <stdlib.h>

static __attribute__((pure)) int popcount(int v)
{
	if (__builtin_expect ( v != 0, 1)) {

		int c = 0;

		while (v) {
			if (v & 1)
				++c;
			v>>=1;
		}
		return c;
	}
	return 0;
}

static __attribute__((pure)) int ctz(int v)
{
	if (__builtin_expect ( v != 0, 1)) {
		int c = 0;
		while (1) {
			if((v & 1))
				break;
			++c;
			v>>=1;
		}
		return c;
	}
	return sizeof v * 8;
}

#define TEST(f0, f1, x) { int r0 = f0(x); int r1=f1(x); \
	printf("[%-3s] C ==> %d vs ASM ==> %d.\n", (r0==r1) ? "OK":"BUG", r0, r1) ; }

int main(int argc, char *argv[])
{
	int v;

	if (argc != 2)
		return 1;

	v = strtol(argv[1], NULL, 16);

	printf("Pop count: ");
	TEST(popcount, __builtin_popcount, v)

	printf("CTZ      : ");
	TEST(ctz, __builtin_ctz, v)

	return 0;
}