Add CRT test

Author: simonlindholm

fuzz-tests/number-theory/CRT.cpp

@@ -0,0 +1,50 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+#define rep(i, a, b) for(int i = a; i < int(b); ++i)
+#define trav(a, v) for(auto& a : v)
+#define all(x) x.begin(), x.end()
+#define sz(x) (int)(x).size()
+
+typedef long long ll;
+typedef pair<int, int> pii;
+typedef vector<int> vi;
+
+#include "../../content/number-theory/CRT.h"
+
+ll rmod(ll a, ll b) { return (a % b + b) % b; }
+
+std::mt19937_64 rng(2);
+
+ll randExp() {
+	int e = rand() % 63; // 64
+	return uniform_int_distribution<ll>(0, (ll)((1ULL << e) - 1))(rng);
+}
+
+int main(int argc, char** argv) {
+	rep(it,0,10000000) {
+		ll a = randExp() * (rand() % 2 ? 1 : -1);
+		ll b = randExp() * (rand() % 2 ? 1 : -1);
+		ll m = randExp() + 1;
+		ll n = randExp() + 1;
+		ll g = __gcd(m, n);
+		if (n * (__int128_t)m > LLONG_MAX) continue;
+		if (n * (__int128_t)m > (1LL << 62) && (abs(a) > m || abs(b) > n)) continue;
+		if ((a - b) % g == 0) {
+			ll r = crt(a, m, b, n);
+			if (rmod(r, m) != rmod(a, m) || rmod(r, n) != rmod(b, n)) {
+				cout << a << endl;
+				cout << b << endl;
+				cout << m << endl;
+				cout << n << endl;
+			}
+			assert(rmod(r, m) == rmod(a, m));
+			assert(rmod(r, n) == rmod(b, n));
+			if (-m < a && a < m && -n < b && b < n) {
+				assert(0 <= r);
+				assert(r < m*n/g);
+			}
+		}
+	}
+	cout<<"Tests passed!"<<endl;
+}