samplebrain/brain/src/aquila/transform/AquilaFft.h

/**
 * @file AquilaFft.h
 *
 * A custom implementation of FFT radix-2 algorithm.
 *
 * This file is part of the Aquila DSP library.
 * Aquila is free software, licensed under the MIT/X11 License. A copy of
 * the license is provided with the library in the LICENSE file.
 *
 * @package Aquila
 * @version 3.0.0-dev
 * @author Zbigniew Siciarz
 * @date 2007-2014
 * @license http://www.opensource.org/licenses/mit-license.php MIT
 * @since 3.0.0
 */

#ifndef AQUILAFFT_H
#define AQUILAFFT_H

#include "Fft.h"
#include <map>
#include <utility>

namespace Aquila
{
    /**
     * ln(2) - needed for calculating number of stages in FFT.
     */
    const double LN_2 = 0.69314718055994530941723212145818;

    /**
     * A custom implementation of FFT radix-2 algorithm.
     */
    class AQUILA_EXPORT AquilaFft : public Fft
    {
    public:
        /**
         * Initializes the transform for a given input length.
         *
         * @param length input signal size (usually a power of 2)
         */
        AquilaFft(std::size_t length):
            Fft(length), fftWiCache()
        {
        }

        /**
         * Destroys the transform object.
         *
         * @todo clear the cache somewhere else, not here!
         */
        ~AquilaFft()
        {
            clearFftWiCache();
        }

        virtual SpectrumType fft(const SampleType x[]);
        virtual void ifft(SpectrumType spectrum, double x[]);

    private:
        /**
         * Complex unit (0.0 + 1.0j).
         */
        static const ComplexType j;

        /**
         * Type of the twiddle factor cache key.
         */
        typedef unsigned int fftWiCacheKeyType;

        /**
         * Type of the twiddle factor cache.
         */
        typedef std::map<fftWiCacheKeyType, ComplexType**> fftWiCacheType;

        /**
         * Twiddle factor cache - implemented as a map.
         */
        fftWiCacheType fftWiCache;

        ComplexType** getCachedFftWi(unsigned int numStages);

        void clearFftWiCache();
    };
}

#endif // AQUILAFFT_H