mzuenni tests

1 files changed, 23 insertions, 0 deletions

diff --git a/content/math/transforms/fft.cpp b/content/math/transforms/fft.cpp
new file mode 100644
index 0000000..2bd95b2
--- /dev/null
+++ b/content/math/transforms/fft.cpp
@@ -0,0 +1,23 @@
+using cplx = complex<double>;
+
+void fft(vector<cplx>& a, bool inv = false) {
+	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]);
+	}
+	static vector<cplx> ws(2, 1);
+	for (static int k = 2; k < n; k *= 2) {
+		ws.resize(n);
+		cplx w = polar(1.0, acos(-1.0) / k);
+		for (int i=k; i<2*k; i++) ws[i] = ws[i/2] * (i % 2 ? w : 1);
+	}
+	for (int s = 1; s < n; s *= 2) {
+		for (int j = 0; j < n; j += 2 * s) {
+			for (int k = 0; k < s; k++) {
+				cplx u = a[j + k], t = a[j + s + k];
+				t *= (inv ? conj(ws[s + k]) : ws[s + k]);
+				a[j + k] = u + t;
+				a[j + s + k] = u - t;
+				if (inv) a[j + k] /= 2, a[j + s + k] /= 2;
+}}}}