| 142 | } |
| 143 | |
| 144 | Num3072 Num3072::GetInverse() const |
| 145 | { |
| 146 | // For fast exponentiation a sliding window exponentiation with repunit |
| 147 | // precomputation is utilized. See "Fast Point Decompression for Standard |
| 148 | // Elliptic Curves" (Brumley, Järvinen, 2008). |
| 149 | |
| 150 | Num3072 p[12]; // p[i] = a^(2^(2^i)-1) |
| 151 | Num3072 out; |
| 152 | |
| 153 | p[0] = *this; |
| 154 | |
| 155 | for (int i = 0; i < 11; ++i) { |
| 156 | p[i + 1] = p[i]; |
| 157 | for (int j = 0; j < (1 << i); ++j) p[i + 1].Square(); |
| 158 | p[i + 1].Multiply(p[i]); |
| 159 | } |
| 160 | |
| 161 | out = p[11]; |
| 162 | |
| 163 | square_n_mul(out, 512, p[9]); |
| 164 | square_n_mul(out, 256, p[8]); |
| 165 | square_n_mul(out, 128, p[7]); |
| 166 | square_n_mul(out, 64, p[6]); |
| 167 | square_n_mul(out, 32, p[5]); |
| 168 | square_n_mul(out, 8, p[3]); |
| 169 | square_n_mul(out, 2, p[1]); |
| 170 | square_n_mul(out, 1, p[0]); |
| 171 | square_n_mul(out, 5, p[2]); |
| 172 | square_n_mul(out, 3, p[0]); |
| 173 | square_n_mul(out, 2, p[0]); |
| 174 | square_n_mul(out, 4, p[0]); |
| 175 | square_n_mul(out, 4, p[1]); |
| 176 | square_n_mul(out, 3, p[0]); |
| 177 | |
| 178 | return out; |
| 179 | } |
| 180 | |
| 181 | void Num3072::Multiply(const Num3072& a) |
| 182 | { |
no test coverage detected