1 files changed, 17 insertions, 0 deletions
diff --git a/content/math/discreteLogarithm.cpp b/content/math/discreteLogarithm.cpp
new file mode 100644
index 0000000..68866e0
--- /dev/null
+++ b/content/math/discreteLogarithm.cpp
@@ -0,0 +1,17 @@
+ll dlog(ll a, ll b, ll m) { //a > 0!
+	ll bound = sqrtl(m) + 1; //memory usage bound < p
+	vector<pair<ll, ll>> vals(bound);
+	for (ll i = 0, e = 1; i < bound; i++, e = (e * a) % m) {
+		vals[i] = {e, i};
+	}
+	vals.emplace_back(m, 0);
+	sort(all(vals));
+	ll fact = powMod(a, m - bound - 1, m);
+
+	for (ll i = 0; i < m; i += bound, b = (b * fact) % m) {
+		auto it = lower_bound(all(vals), pair<ll, ll>{b, 0});
+		if (it->first == b) {
+			return (i + it->second) % m;
+	}}
+	return -1;
+}