updated tcr

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;
+}}}}