librubberband/src/dsp/SincWindow.h

/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */

/*
    Rubber Band
    An audio time-stretching and pitch-shifting library.
    Copyright 2007-2011 Chris Cannam.
    
    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License as
    published by the Free Software Foundation; either version 2 of the
    License, or (at your option) any later version.  See the file
    COPYING included with this distribution for more information.
*/

#ifndef _RUBBERBAND_SINC_WINDOW_H_
#define _RUBBERBAND_SINC_WINDOW_H_

#include <cmath>
#include <iostream>
#include <cstdlib>
#include <map>

#include "system/sysutils.h"
#include "system/VectorOps.h"
#include "system/Allocators.h"

namespace RubberBand {

template <typename T>
class SincWindow
{
public:
    /**
     * Construct a sinc windower which produces a window of size n
     * containing the values of sinc(x) with x=0 at index n/2, such
     * that the distance from -pi to pi (the point at which the sinc
     * function first crosses zero, for negative and positive
     * arguments respectively) is p samples.
     */
    SincWindow(int n, int p) : m_size(n), m_p(p), m_cache(0) {
        encache();
    }
    SincWindow(const SincWindow &w) : m_size(w.m_size), m_p(w.m_p), m_cache(0) {
        encache();
    }
    SincWindow &operator=(const SincWindow &w) {
	if (&w == this) return *this;
	m_size = w.m_size;
	m_p = w.m_p;
        m_cache = 0;
	encache();
	return *this;
    }
    virtual ~SincWindow() {
        deallocate(m_cache);
    }

    /**
     * Regenerate the sinc window with the same size, but a new scale
     * (the p value is interpreted as for the argument of the same
     * name to the constructor).  If p is unchanged from the previous
     * value, do nothing (quickly).
     */
    inline void rewrite(int p) {
        if (m_p == p) return;
        m_p = p;
        encache();
    }
    
    inline void cut(T *const R__ dst) const {
        v_multiply(dst, m_cache, m_size);
    }

    inline void cut(const T *const R__ src, T *const R__ dst) const {
        v_multiply(dst, src, m_cache, m_size);
    }

    inline void add(T *const R__ dst, T scale) const {
        v_add_with_gain(dst, m_cache, m_size, scale);
    }

    inline T getArea() const { return m_area; }
    inline T getValue(int i) const { return m_cache[i]; }

    inline int getSize() const { return m_size; }
    inline int getP() const { return m_p; }

    /**
     * Write a sinc window of size n with scale p (the p value is
     * interpreted as for the argument of the same name to the
     * constructor).
     */
    static
    void write(T *const R__ dst, const int n, const int p) {
        const int half = n/2;
        writeHalf(dst, n, p);
        int target = half - 1;
        for (int i = half + 1; i < n; ++i) {
            dst[target--] = dst[i];
        }
        const T twopi = 2. * M_PI;
        T arg = T(half) * twopi / p;
        dst[0] = sin(arg) / arg;
    }

protected:
    int m_size;
    int m_p;
    T *R__ m_cache;
    T m_area;

    /**
     * Write the positive half (i.e. n/2 to n-1) of a sinc window of
     * size n with scale p (the p value is interpreted as for the
     * argument of the same name to the constructor). The negative
     * half (indices 0 to n/2-1) of dst is left unchanged.
     */
    static
    void writeHalf(T *const R__ dst, const int n, const int p) {
        const int half = n/2;
        const T twopi = 2. * M_PI;
        dst[half] = T(1.0);
        for (int i = 1; i < half; ++i) {
            T arg = T(i) * twopi / p;
            dst[half+i] = sin(arg) / arg;
        }
    }
    
    void encache() {
        if (!m_cache) {
            m_cache = allocate<T>(m_size);
        }

        write(m_cache, m_size, m_p);
	
        m_area = 0;
        for (int i = 0; i < m_size; ++i) {
            m_area += m_cache[i];
        }
        m_area /= m_size;
    }
};

}

#endif