Speed test

gistfile1.c

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

#define HOWMUCH 100000000
#define RANDOMBITS 4

static uint64_t stats[32];
static uint64_t stats2[32];
static uint32_t flags[HOWMUCH];

int main()
{
	time_t start;

	/* generate flags */

	printf("generating flags... ");

	start = time(NULL);

	for (uint64_t i = 0; i < HOWMUCH; i++) {
		/* create random flag */
		for (uint32_t j = 0; j < RANDOMBITS; j++) {
			flags[i] |= 1 << (random() % 32);
		}
	}

	printf("%ld s\n", time(NULL) - start);

	printf("using cycle... ");

	start = time(NULL);

	for (uint64_t i = 0; i < HOWMUCH; i++) {
		for (int x = 0; x < 32; x++) {
			if (flags[i] & (1 << x)) {
				stats[x]++;
			}
		}
	}

	printf("%ld s\n", time(NULL) - start);

	for (int x = 0; x < 32; x++) {
		printf("%ld ", stats[x]);
	}
	printf("\n");

	printf("using builtin... ");

	start = time(NULL);

	for (uint64_t i = 0; i < HOWMUCH; i++) {
		uint32_t flag = flags[i];
		int offset = 0;

		while (flag > 0) {
			int zeroes = __builtin_ctzl(flag);
			int moveby = zeroes+1;

			stats2[offset + zeroes]++;

			if (moveby == 32) {
				flag = 0;
			} else {
				flag >>= moveby;
				offset += moveby;
			}
		}
	}

	printf("%ld s\n", time(NULL) - start);

	for (int x = 0; x < 32; x++) {
		printf("%ld ", stats2[x]);
	}
	printf("\n");

	for (int x = 0; x < 32; x++) {
		if (stats[x] != stats2[x]) {
			printf("%i bit NOT SAME (%ld != %ld)\n", x, stats[x], stats2[x]);
			return 0;
		}
	}
	printf("SAME\n");


	return 0;
}