add divSum (sum of floor linear)

1 files changed, 48 insertions, 0 deletions

diff --git a/test/math/divSum.cpp b/test/math/divSum.cpp
new file mode 100644
index 0000000..1f82387
--- /dev/null
+++ b/test/math/divSum.cpp
@@ -0,0 +1,48 @@
+#include "../util.h"
+#include <math/divSum.cpp>
+
+ll naive(ll n, ll m, ll a, ll b){
+	ll ans = 0;
+	for(ll i = 0; i < n; i++){
+		ans += (a*i+b)/m;
+	}
+	return ans;
+}
+
+void stress_test() {
+	ll queries = 0;
+	for (ll i = 0; i < 10'000; i++) {
+		int n = Random::integer<int>(1, 100);
+		int m = Random::integer<int>(1, 100);
+		int a = Random::integer<int>(0, 100);
+		int b = Random::integer<int>(0, 100);
+		ll expected = naive(n, m, a, b);
+		ll got = divSum(n, m, a, b);
+		if (got != expected) cerr << "got: " << got << ", expected: " << expected << FAIL;
+		queries++;
+	}
+	cerr << "tested queries: " << queries << endl;
+}
+
+constexpr int N = 1'000'000;
+void performance_test() {
+	timer t;
+	hash_t hash = 0;
+	for (int operations = 0; operations < N; operations++) {
+		ll n = Random::integer<ll>(1, 1'000'000'000);
+		ll m = Random::integer<ll>(1, 1'000'000'000);
+		ll a = Random::integer<ll>(0, 1'000'000'000);
+		ll b = Random::integer<ll>(0, 1'000'000'000);
+		t.start();
+		hash += divSum(n, m, a, b);
+		t.stop();
+	}
+	if (t.time > 750) cerr << "too slow: " << t.time << FAIL;
+	cerr << "tested performance: " << t.time << "ms (hash: " << hash << ")" << endl;
+}
+
+int main() {
+	stress_test();
+	performance_test();
+}
+