✨ adds hash for 2^61-1

algorithms/data-structures/big-big-hash.cpp

@@ -0,0 +1,32 @@
+const ll MOD = (1ll<<61) - 1;
+ll mulmod(ll a, ll b) {
+	const static ll LOWER = (1ll<<30) - 1, GET31 = (1ll<<31) - 1;
+	ll l1 = a&LOWER, h1 = a>>30, l2 = b&LOWER, h2 = b>>30;
+	ll m = l1*h2 + l2*h1, h = h1*h2;
+	ll ans = l1*l2 + (h>>1) + ((h&1)<<60) + (m>>31) + ((m&GET31)<<30) + 1;
+	ans = (ans&MOD) + (ans>>61), ans = (ans&MOD) + (ans>>61);
+	return ans - 1;
+}
+
+mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count()); 
+
+ll uniform(ll l, ll r) {
+	uniform_int_distribution<ll> uid(l, r);
+	return uid(rng);
+}
+
+struct str_hash {
+	static ll P;
+	vector<ll> h, p;
+	str_hash(string s) : h(s.size()), p(s.size()) {
+		p[0] = 1, h[0] = s[0];
+		for (int i = 1; i < s.size(); i++)
+			p[i] = mulmod(p[i - 1], P), h[i] = (mulmod(h[i - 1], P) + s[i])%MOD;
+	}
+	ll operator()(int l, int r) { // retorna hash s[l...r]
+		ll hash = h[r] - (l ? mulmod(h[l - 1], p[r - l + 1]) : 0);
+		return hash < 0 ? hash + MOD : hash;
+	}
+};
+
+ll str_hash::P = uniform(256, MOD - 1); // l > |sigma|

algorithms/data-structures/big-big-hash.tex

@@ -0,0 +1 @@
+\subsection{Hash module $2^{61}-1$}