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#include "library/number/montogomery.hpp"
#ifndef SUISEN_MONTGOMERY #define SUISEN_MONTGOMERY #include <cassert> #include <cstdint> #include <limits> namespace suisen { namespace internal::montgomery { template <typename Int, typename DInt> struct Montgomery { private: static constexpr uint32_t bits = std::numeric_limits<Int>::digits; static constexpr Int mask = ~Int(0); // R = 2**32 or 2**64 // 1. N is an odd number // 2. N < R // 3. gcd(N, R) = 1 // 4. R * R2 - N * N2 = 1 // 5. 0 < R2 < N // 6. 0 < N2 < R Int N, N2, R2; // RR = R * R (mod N) Int RR; public: constexpr Montgomery() = default; explicit constexpr Montgomery(Int N) : N(N), N2(calcN2(N)), R2(calcR2(N, N2)), RR(calcRR(N)) { assert(N & 1); } // @returns t * R (mod N) constexpr Int make(Int t) const { return reduce(static_cast<DInt>(t) * RR); } // @returns T * R^(-1) (mod N) constexpr Int reduce(DInt T) const { // 0 <= T < RN // Note: // 1. m = T * N2 (mod R) // 2. 0 <= m < R DInt m = modR(static_cast<DInt>(modR(T)) * N2); // Note: // T + m * N = T + T * N * N2 = T + T * (R * R2 - 1) = 0 (mod R) // => (T + m * N) / R is an integer. // => t * R = T + m * N = T (mod N) // => t = T R^(-1) (mod N) DInt t = divR(T + m * N); // Note: // 1. 0 <= T < RN // 2. 0 <= mN < RN (because 0 <= m < R) // => 0 <= T + mN < 2RN // => 0 <= t < 2N return t >= N ? t - N : t; } constexpr Int add(Int A, Int B) const { return (A += B) >= N ? A - N : A; } constexpr Int sub(Int A, Int B) const { return (A -= B) < 0 ? A + N : A; } constexpr Int mul(Int A, Int B) const { return reduce(static_cast<DInt>(A) * B); } constexpr Int div(Int A, Int B) const { return reduce(static_cast<DInt>(A) * inv(B)); } constexpr Int inv(Int A) const; // TODO: Implement constexpr Int pow(Int A, long long b) const { Int P = make(1); for (; b; b >>= 1) { if (b & 1) P = mul(P, A); A = mul(A, A); } return P; } private: static constexpr Int divR(DInt t) { return t >> bits; } static constexpr Int modR(DInt t) { return t & mask; } static constexpr Int calcN2(Int N) { // - N * N2 = 1 (mod R) // N2 = -N^{-1} (mod R) // calculates N^{-1} (mod R) by Newton's method DInt invN = N; // = N^{-1} (mod 2^2) for (uint32_t cur_bits = 2; cur_bits < bits; cur_bits *= 2) { // loop invariant: invN = N^{-1} (mod 2^cur_bits) // x = a^{-1} mod m => x(2-ax) = a^{-1} mod m^2 because: // ax = 1 (mod m) // => (ax-1)^2 = 0 (mod m^2) // => 2ax - a^2x^2 = 1 (mod m^2) // => a(x(2-ax)) = 1 (mod m^2) invN = modR(invN * modR(2 - N * invN)); } assert(modR(N * invN) == 1); return modR(-invN); } static constexpr Int calcR2(Int N, Int N2) { // R * R2 - N * N2 = 1 // => R2 = (1 + N * N2) / R return divR(1 + static_cast<DInt>(N) * N2); } static constexpr Int calcRR(Int N) { return -DInt(N) % N; } }; } // namespace internal::montgomery using Montgomery32 = internal::montgomery::Montgomery<uint32_t, uint64_t>; using Montgomery64 = internal::montgomery::Montgomery<uint64_t, __uint128_t>; } // namespace suisen #endif // SUISEN_MONTGOMERY
#line 1 "library/number/montogomery.hpp" #include <cassert> #include <cstdint> #include <limits> namespace suisen { namespace internal::montgomery { template <typename Int, typename DInt> struct Montgomery { private: static constexpr uint32_t bits = std::numeric_limits<Int>::digits; static constexpr Int mask = ~Int(0); // R = 2**32 or 2**64 // 1. N is an odd number // 2. N < R // 3. gcd(N, R) = 1 // 4. R * R2 - N * N2 = 1 // 5. 0 < R2 < N // 6. 0 < N2 < R Int N, N2, R2; // RR = R * R (mod N) Int RR; public: constexpr Montgomery() = default; explicit constexpr Montgomery(Int N) : N(N), N2(calcN2(N)), R2(calcR2(N, N2)), RR(calcRR(N)) { assert(N & 1); } // @returns t * R (mod N) constexpr Int make(Int t) const { return reduce(static_cast<DInt>(t) * RR); } // @returns T * R^(-1) (mod N) constexpr Int reduce(DInt T) const { // 0 <= T < RN // Note: // 1. m = T * N2 (mod R) // 2. 0 <= m < R DInt m = modR(static_cast<DInt>(modR(T)) * N2); // Note: // T + m * N = T + T * N * N2 = T + T * (R * R2 - 1) = 0 (mod R) // => (T + m * N) / R is an integer. // => t * R = T + m * N = T (mod N) // => t = T R^(-1) (mod N) DInt t = divR(T + m * N); // Note: // 1. 0 <= T < RN // 2. 0 <= mN < RN (because 0 <= m < R) // => 0 <= T + mN < 2RN // => 0 <= t < 2N return t >= N ? t - N : t; } constexpr Int add(Int A, Int B) const { return (A += B) >= N ? A - N : A; } constexpr Int sub(Int A, Int B) const { return (A -= B) < 0 ? A + N : A; } constexpr Int mul(Int A, Int B) const { return reduce(static_cast<DInt>(A) * B); } constexpr Int div(Int A, Int B) const { return reduce(static_cast<DInt>(A) * inv(B)); } constexpr Int inv(Int A) const; // TODO: Implement constexpr Int pow(Int A, long long b) const { Int P = make(1); for (; b; b >>= 1) { if (b & 1) P = mul(P, A); A = mul(A, A); } return P; } private: static constexpr Int divR(DInt t) { return t >> bits; } static constexpr Int modR(DInt t) { return t & mask; } static constexpr Int calcN2(Int N) { // - N * N2 = 1 (mod R) // N2 = -N^{-1} (mod R) // calculates N^{-1} (mod R) by Newton's method DInt invN = N; // = N^{-1} (mod 2^2) for (uint32_t cur_bits = 2; cur_bits < bits; cur_bits *= 2) { // loop invariant: invN = N^{-1} (mod 2^cur_bits) // x = a^{-1} mod m => x(2-ax) = a^{-1} mod m^2 because: // ax = 1 (mod m) // => (ax-1)^2 = 0 (mod m^2) // => 2ax - a^2x^2 = 1 (mod m^2) // => a(x(2-ax)) = 1 (mod m^2) invN = modR(invN * modR(2 - N * invN)); } assert(modR(N * invN) == 1); return modR(-invN); } static constexpr Int calcR2(Int N, Int N2) { // R * R2 - N * N2 = 1 // => R2 = (1 + N * N2) / R return divR(1 + static_cast<DInt>(N) * N2); } static constexpr Int calcRR(Int N) { return -DInt(N) % N; } }; } // namespace internal::montgomery using Montgomery32 = internal::montgomery::Montgomery<uint32_t, uint64_t>; using Montgomery64 = internal::montgomery::Montgomery<uint64_t, __uint128_t>; } // namespace suisen