fastrand/perf.cpp

#include <cstdio>
#include <cstdlib>
#include <chrono>
#include <cassert>
#include "fastrand.h"

#define N 10000000
#define M 99999999 // M > N
#define FROM 100
#define TO 576

int main() {
	assert(M > N); // M > N

	// Init
	srand((unsigned int)time(NULL));
	rand_state rs = init_rand();
	uint32_t sum = 0; // to avoid compiler optimizing out stuff

	printf("Full range generation perf - %d number of cases:\n", N);

	auto t0 = std::chrono::high_resolution_clock::now();

	// rand
	for (int i = 0; i < N; ++i) {
		sum += rand();
	}

	auto t1 = std::chrono::high_resolution_clock::now();

	// arc4
	for (int i = 0; i < N; ++i) {
		sum += arc4random();
	}

	auto t2 = std::chrono::high_resolution_clock::now();

	// lcg
	for (int i = 0; i < N; ++i) {
		sum += lcg(&rs);
	}

	auto t3 = std::chrono::high_resolution_clock::now();

	// results 1

	auto rand_elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(t1 - t0);
	auto arc4_elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(t2 - t1);
	auto lcg_elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(t3 - t2);

	printf("Time (rand): %.3f ms.\n", rand_elapsed.count() * 1e-6);
	printf("Time (arc4): %.3f ms.\n", arc4_elapsed.count() * 1e-6);
	printf("Time (lcg): %.3f ms.\n", lcg_elapsed.count() * 1e-6);

	printf("Modulo VS nomod perf for rand_between (both LCG) - %d number of cases:\n", M);

	auto t4 = std::chrono::high_resolution_clock::now();

	// lcg + modulo
	for (int i = 0; i < M; ++i) {
		sum += FROM + (lcg(&rs) % (TO - FROM));
	}

	auto t5 = std::chrono::high_resolution_clock::now();

	// rand_between (also LCG, but no modulus)
	for (int i = 0; i < M; ++i) {
		sum += rand_between(&rs, FROM, TO);
	}

	auto t6 = std::chrono::high_resolution_clock::now();

	// results 2

	auto mod_elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(t5 - t4);
	auto between_elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(t6 - t5);

	uint32_t choice = rand_between(&rs, FROM, TO);
	printf("lcg + modulo [%u, %u): %.3f ms.\n", FROM, TO, mod_elapsed.count() * 1e-6);
	printf("rand_between [%u, %u): %.3f ms.\n", FROM, TO, between_elapsed.count() * 1e-6);

	// checksum - avoid optimizing out loops

	printf("Checksum: 0x%x\n", sum);

	return 0;
}