tests/bench/sieve.c


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/* primes below N. the same loops as tests/bench/sieve.zc.
   word: one int64 flag per number (what zc's fast path can do).
   byte: one byte per number, the representation a C sieve would actually use.
   the count is 9592 either way.
   usage: sieve word|byte REPS */
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>

enum { N = 100000, EXPECT = 9592 };

static int sieve_word(int64_t *restrict f)
{
	int c = 0;
	for (int i = 2; i < N; i++) f[i] = 1;
	for (int i = 2; (long long)i * i < N; i++)
		if (f[i])
			for (int j = i * i; j < N; j += i) f[j] = 0;
	for (int i = 2; i < N; i++) c += (int)f[i];
	return c;
}

static int sieve_byte(unsigned char *restrict f)
{
	int c = 0;
	for (int i = 2; i < N; i++) f[i] = 1;
	for (int i = 2; (long long)i * i < N; i++)
		if (f[i])
			for (int j = i * i; j < N; j += i) f[j] = 0;
	for (int i = 2; i < N; i++) c += f[i];
	return c;
}

int main(int argc, char **argv)
{
	int reps, r = 0, k, byte;
	int64_t *w = 0;
	unsigned char *b = 0;
	if (argc != 3) return 2;
	byte = argv[1][0] == 'b';
	reps = atoi(argv[2]);
	if (byte) b = malloc(N);
	else w = malloc((size_t)N * sizeof *w);
	if (!w && !b) return 3;
	for (k = 0; k < reps; k++) {
		r = byte ? sieve_byte(b) : sieve_word(w);
		/* the stores have to happen: the next pass must see a clobbered buffer */
		__asm__ __volatile__("" : "+r"(r) : "r"(byte ? (void *)b : (void *)w) : "memory");
	}
	if (r != EXPECT) {
		fprintf(stderr, "bad %d\n", r);
		return 1;
	}
	printf("%d\n", r);
	free(w);
	free(b);
	return 0;
}