Initial data commit

Task/Fast-Fourier-transform/Delphi/fast-fourier-transform.delphi

@@ -0,0 +1,88 @@
+program Fast_Fourier_transform;
+
+{$APPTYPE CONSOLE}
+
+uses
+  System.SysUtils,
+  System.VarCmplx,
+  System.Math;
+
+function BitReverse(n: UInt64; bits: Integer): UInt64;
+var
+  count, reversedN: UInt64;
+begin
+  reversedN := n;
+  count := bits - 1;
+
+  n := n shr 1;
+
+  while n > 0 do
+  begin
+    reversedN := (reversedN shl 1) or (n and 1);
+    dec(count);
+    n := n shr 1;
+  end;
+
+  Result := ((reversedN shl count) and ((1 shl bits) - 1));
+end;
+
+procedure FFT(var buffer: TArray<Variant>);
+var
+  j, bits: Integer;
+  tmp: Variant;
+begin
+  bits := Trunc(Log2(length(buffer)));
+
+  for j := 1 to High(buffer) do
+  begin
+    var swapPos := BitReverse(j, bits);
+    if swapPos <= j then
+      Continue;
+
+    tmp := buffer[j];
+    buffer[j] := buffer[swapPos];
+    buffer[swapPos] := tmp;
+  end;
+
+  var N := 2;
+  while N <= Length(buffer) do
+  begin
+    var i := 0;
+    while i < Length(buffer) do
+    begin
+      for var k := 0 to N div 2 - 1 do
+      begin
+        var evenIndex := i + k;
+        var oddIndex := i + k + (N div 2);
+        var _even := buffer[evenIndex];
+        var _odd := buffer[oddIndex];
+        var term := -2 * PI * k / N;
+        var _exp := VarComplexCreate(Cos(term), Sin(term)) * _odd;
+
+        buffer[evenIndex] := _even + _exp;
+        buffer[oddIndex] := _even - _exp;
+      end;
+      i := i + N;
+    end;
+    N := N shl 1;
+  end;
+
+end;
+
+const
+  input: array of Double = [1.0, 1.0, 1.0, 1.0, 0.0, 0.0, 0.0, 0.0];
+
+var
+  inputc: TArray<Variant>;
+
+begin
+  SetLength(inputc, length(input));
+  for var i := 0 to High(input) do
+    inputc[i] := VarComplexCreate(input[i]);
+
+  FFT(inputc);
+
+  for var c in inputc do
+    writeln(c);
+  readln;
+end.