diff options
Diffstat (limited to 'math/transforms/fft.cpp')
| -rw-r--r-- | math/transforms/fft.cpp | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/math/transforms/fft.cpp b/math/transforms/fft.cpp new file mode 100644 index 0000000..4540ed8 --- /dev/null +++ b/math/transforms/fft.cpp @@ -0,0 +1,20 @@ +using cplx = complex<double>; // Eigene Implementierung ist schneller. + +void fft(vector<cplx>& a, bool inverse = 0) { + int n = sz(a); + for (int i = 0, j = 1; j < n - 1; ++j) { + for (int k = n >> 1; k > (i ^= k); k >>= 1); + if (j < i) swap(a[i], a[j]); + } + for (int s = 1; s < n; s *= 2) { + double angle = PI / s * (inverse ? -1 : 1); + cplx ws(cos(angle), sin(angle)); + for (int j = 0; j < n; j+= 2 * s) { + cplx w = 1; + for (int k = 0; k < s; k++) { + cplx u = a[j + k], t = a[j + s + k] * w; + a[j + k] = u + t; + a[j + s + k] = u - t; + if (inverse) a[j + k] /= 2, a[j + s + k] /= 2; + w *= ws; +}}}} |