Common::RDFT Class Reference

(Inverse) Real Discrete Fourier Transform. More...

#include <rdft.h>

Public Types
enum	TransformType { DFT_R2C, IDFT_C2R, IDFT_R2C, DFT_C2R }

Public Member Functions
	RDFT (int bits, TransformType trans)
void	calc (float *data)

Detailed Description

(Inverse) Real Discrete Fourier Transform.

Used in audio:

• QDM2

Used in engines:

• scumm

It has four modes:

Below, n = 1 << bits

(I)DFT_R2C: input: n real floats output: n/2 complex floats (stored as real part followed by imag part).

The output represents the first half of the (I)DFT of the input. If F is the complex (I)DFT of the input, then output[0] = F[0] + i * F[n/2] and output[k] = F[k] for k = 1 .. n/2-1. Note that F[0] and F[k] are real since the input is real, and the remaining values of F can be reconstructed from symmetry if desired.

(I)DFT_C2R: input: n/2 complex floats output: n real floats

The input encodes a complex vector x of length n that has the required symmetry to have a real (I)DFT: x[0] = Re(input[0]) x[k] = input[k] for k = 1 .. n/2-1 x[n/2] = Im(input[0]) x[k] = conj(input[n-k]) for k = n/2+1 .. n-1 The output is then the real (I)DFT of x, divided by 2.

TODO: Is this division by 2 intentional?

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The documentation for this class was generated from the following file:

• common/rdft.h