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add: assert of convolution #142

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Merged
yosupo06 merged 3 commits into from
Mar 15, 2023
Merged

add: assert of convolution #142

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bc8789c
add: assert of convolution_ll
TumoiYorozu May 31, 2022
db0fc0d
add: assert of convolution_fft
TumoiYorozu May 31, 2022
f5c30a3
Add comment to static_assert
TumoiYorozu Mar 7, 2023
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7 changes: 7 additions & 0 deletions atcoder/convolution.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -199,6 +199,7 @@ template <class mint, internal::is_static_modint_t<mint>* = nullptr>
std::vector<mint> convolution_fft(std::vector<mint> a, std::vector<mint> b) {
int n = int(a.size()), m = int(b.size());
int z = 1 << internal::ceil_pow2(n + m - 1);
assert(mint::mod() % z == 1);
a.resize(z);
internal::butterfly(a);
b.resize(z);
Expand Down Expand Up @@ -274,6 +275,12 @@ std::vector<long long> convolution_ll(const std::vector<long long>& a,
internal::inv_gcd(MOD1 * MOD3, MOD2).second;
static constexpr unsigned long long i3 =
internal::inv_gcd(MOD1 * MOD2, MOD3).second;

static constexpr int MAX_AB_BIT = 24;
static_assert(MOD1 % (1ull << MAX_AB_BIT) == 1, "MOD1 isn't enough to support an array length of 2^24.");
static_assert(MOD2 % (1ull << MAX_AB_BIT) == 1, "MOD2 isn't enough to support an array length of 2^24.");
static_assert(MOD3 % (1ull << MAX_AB_BIT) == 1, "MOD3 isn't enough to support an array length of 2^24.");
assert(a.size() + b.size() - 1 <= (1ull << MAX_AB_BIT));

auto c1 = convolution<MOD1>(a, b);
auto c2 = convolution<MOD2>(a, b);
Expand Down