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Diffstat (limited to 'content/math/transforms/fftMul.cpp')
| -rw-r--r-- | content/math/transforms/fftMul.cpp | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/content/math/transforms/fftMul.cpp b/content/math/transforms/fftMul.cpp new file mode 100644 index 0000000..660ed79 --- /dev/null +++ b/content/math/transforms/fftMul.cpp @@ -0,0 +1,15 @@ +vector<cplx> mul(vector<ll>& a, vector<ll>& b) { + int n = 1 << (__lg(sz(a) + sz(b) - 1) + 1); + vector<cplx> c(all(a)), d(n); + c.resize(n); + for (int i = 0; i < sz(b); i++) c[i] = {real(c[i]), b[i]}; + fft(c); + for (int i = 0; i < n; i++) { + int j = (n - i) & (n - 1); + cplx x = (c[i] + conj(c[j])) / cplx{2, 0}; //fft(a)[i]; + cplx y = (c[i] - conj(c[j])) / cplx{0, 2}; //fft(b)[i]; + d[i] = x * y; + } + fft(d, true); + return d; +} |