Fixes + log test

Author: adamant-pwn

cp-algo/math/poly.hpp

@@ -167,7 +167,7 @@ namespace cp_algo::math {
 
         poly_t log(size_t n) const { // calculate log p(x) mod x^n
             assert(a[0] == T(1));
-            return (deriv().mod_xk(n) * inv(n)).integr().mod_xk(n);
+            return (mod_xk(n).deriv() * inv(n)).mod_xk(n - 1).integr();
         }
 
         poly_t exp(size_t n) const { // calculate exp p(x) mod x^n
@@ -547,6 +547,7 @@ namespace cp_algo::math {
 
         // Return {P0, P1}, where P(x) = P0(x) + xP1(x)
         std::array<poly_t, 2> bisect(size_t n) const {
+            n = std::min(n, size(a));
             std::deque<T> res[2];
             for(size_t i = 0; i < n; i++) {
                 res[i % 2].push_back(a[i]);

cp-algo/math/poly/impl/div.hpp

@@ -111,8 +111,9 @@ namespace cp_algo::math::poly::impl {
         inv_inplace(qq, (n + 1) / 2);
         auto qqf = fft::dft<base>(qq.a, N);
 
-        auto A = q0f * qqf;
-        auto B = q1f * qqf;
+        std::deque<base> A((n + 1) / 2), B((n + 1) / 2);
+        q0f.mul(fft::dft<base>(qqf), A, (n + 1) / 2);
+        q1f.mul(qqf, B, (n + 1) / 2);
         p.a.resize(n + 1);
         for(size_t i = 0; i < n; i += 2) {
             p.a[i] = A[i / 2];

verify/poly/log.test.cpp

@@ -0,0 +1,30 @@
+// @brief Log of Power Series
+#define PROBLEM "https://judge.yosupo.jp/problem/log_of_formal_power_series"
+#pragma GCC optimize("Ofast,unroll-loops")
+#include "cp-algo/math/poly.hpp"
+#include <bits/stdc++.h>
+
+using namespace std;
+using namespace cp_algo::math;
+
+const int mod = 998244353;
+using base = modint<mod>;
+using polyn = poly_t<base>;
+
+void solve() {
+    int n;
+    cin >> n;
+    vector<base> a(n);
+    copy_n(istream_iterator<base>(cin), n, begin(a));
+    polyn(a).log(n).print(n);
+}
+
+signed main() {
+    //freopen("input.txt", "r", stdin);
+    ios::sync_with_stdio(0);
+    cin.tie(0);
+    int t = 1;
+    while(t--) {
+        solve();
+    }
+}