1 files changed, 47 insertions, 0 deletions
diff --git a/test/math/cycleDetection.cpp b/test/math/cycleDetection.cpp
new file mode 100644
index 0000000..bf57aed
--- /dev/null
+++ b/test/math/cycleDetection.cpp
@@ -0,0 +1,47 @@
+#include "../util.h"
+#include <datastructures/pbds.cpp>
+#include <math/cycleDetection.cpp>
+
+pair<ll, ll> naive(ll x0, function<ll(ll)> f) {
+	map<ll, ll> seen;
+	ll d = 0;
+	while (seen.find(x0) == seen.end()) {
+		seen[x0] = d;
+		d++;
+		x0 = f(x0);
+	}
+	return {seen[x0], d - seen[x0]};
+}
+
+void stress_test() {
+	ll queries = 0;
+	for (ll i = 0; i < 1000'000; i++) {
+		int m = Random::integer<int>(1, 100);
+		int c = Random::integer<int>(0, m);
+		auto f = [&](ll x){return (x*x + c) % m;};
+		int x0 = Random::integer<int>(0, m);
+		auto got = cycleDetection(x0, f);
+		auto expected = naive(x0, f);
+		if (got != expected) cerr << "error: " << got.first << " " << got.second << " " << expected.first << " " << expected.second << FAIL;
+		queries += got.second;
+	}
+	cerr << "tested queries: " << queries << endl;
+}
+
+constexpr ll M = 18'086'183;
+void performance_test() {
+	timer t;
+	auto f = [&](ll x){return (1337*x + 42) % M;};
+	t.start();
+	auto [a, b] = cycleDetection(42, f);
+	t.stop();
+	hash_t hash = a + b;
+	if (t.time > 500) cerr << "too slow: " << t.time << FAIL;
+	cerr << "tested performance: " << t.time << "ms (hash: " << hash << ")" << endl;
+}
+
+int main() {
+	stress_test();
+	performance_test();
+}
+