audio/utilities/Resample.cc

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/*
 * Copyright (c) 1992-2001 by Sun Microsystems, Inc.
 * All rights reserved.
 */

#pragma ident   "%Z%%M% %I% %E% SMI"

/*
 * This is a impementation of sampling rate conversion for low-passed signals.
 *
 * To convert the input signal of sampling rate of fi to another rate of fo,
 * the least common multiple of fi and fo is derived first:
 *  fm = L * fi = M * fo.
 * Then the input signal is up-sampled to fm by inserting (L -1) zero valued
 * samples after each input sample, low-pass filtered, and down-smapled by
 * saving one sample for every M samples. The implementation takes advantages
 * of the (L - 1) zero values in the filter input and the (M - 1) output
 * samples to be disregarded.
 *
 * If L = 1 or M = 1, a simpler decimation or interpolation is used.
 */
#include <memory.h>
#include <math.h>

#include <Resample.h>

extern "C" {
    char *bcopy(char *, char *, int);
    char *memmove(char *, char *, int);
}

#define BCOPY(src, dest, num) memmove(dest, src, num)

// convolve(), short2double() and double2short() are defined in Fir.cc.
extern double convolve(double *, double *, int);
extern void short2double(double *, short *, int);
extern short double2short(double);

// generate truncated ideal LPF
static void sinc_coef(int   fold,   // sample rate change
    int order,          // LP FIR filter order
    double  *coef)          // filter coefficients
{
    int i;
    float   alpha;
    double  bandwidth = M_PI / fold; // digital bandwidth of pass band

    int half = order >> 1;
    if (order & 1) {        // order is odd, center = half + 0.5
        float center = half + 0.5;
        for (i = 0; i <= half; i++) {
            alpha = center - i;
            coef[i] = sin(bandwidth * alpha) / (M_PI * alpha);
        }
    } else {    // order is even, center = half
        for (i = 0; i < half; i++) {
            alpha = half - i;
            coef[i] = sin(bandwidth * alpha) / (M_PI * alpha);
        }
        coef[i++] = bandwidth / M_PI;
    }
    for (; i <= order; i++)     // symmetric FIR
        coef[i] = coef[order - i];
}

/*
 * poly_conv() = coef[0] * data[length - 1] +
 *       coef[inc_coef] * data[length - 2] +
 *       ...
 *       coef[(length - 1) * inc_coef] * data[0] +
 *
 * convolution of coef[order + 1] and data[length] up-sampled by a factor
 * of inc_coef. The terms of coef[1, 2, ... inc_coef - 1] multiplying 0
 * are ignored.
 */
// polyphase filter convolution
double
poly_conv(double    *coef,      // filter coef array
        int     order,      // filter order
        int     inc_coef,   // 1-to-L up-sample for data[length]
        double  *data,      // data array
        int     length)     // data array length
{
    if ((order < 0) || (inc_coef < 1) || (length < 1))
        return (0.0);
    else {
        double sum = 0.0;
        double *coef_end = coef + order;
        double *data_end = data + length;
        while ((coef <= coef_end) && (data < data_end)) {
            sum += *coef * *--data_end;
            coef += inc_coef;
        }
        return (sum);
    }
}

int
gcf(int a, int b)       // greatest common factor between a and b
{
    int remainder = a % b;
    return (remainder == 0)? b : gcf(b, remainder);
}

void ResampleFilter::
updateState(
    double *in,
    int size)
{
    if (up <= 1)
        Fir::updateState(in, size);
    else if (size >= num_state)
        memcpy(state, in + size - num_state,
            num_state * sizeof (double));
    else {
        int old = num_state - size;
        BCOPY((char *)(state + size), (char *)state,
            old * sizeof (double));
        memcpy(state + old, in, size * sizeof (double));
    }
}

ResampleFilter::            // constructor
ResampleFilter(
    int rate_in,            // sampling rate of input signal
    int rate_out)           // sampling rate of output signal
{
    // filter sampling rate = common multiple of rate_in and rate_out
    int commonfactor = gcf(rate_in, rate_out);
    up = rate_out / commonfactor;
    down = rate_in / commonfactor;

    int fold = (up > down)? up : down;  // take the bigger rate change
    order = (fold << 4) - 2;        // filter order = fold * 16 - 2
    coef = new double[order + 1];
    sinc_coef(fold, order, coef);       // required bandwidth = PI/fold

    if (up > 1) {               // need (order/up) states
        num_state = (order + up  - 1) / up;
        state = new double[num_state];
        for (int i = 0; i < num_state; i++) // reset states
            state[i] = 0.0;
    } else {
        num_state = order;
        state = new double[order];  // need order states
        resetState();
    }
    delay = (order + 1) >> 1;   // assuming symmetric FIR
    down_offset = 0;
    up_offset = 0;
}

// down-to-1 decimation
int ResampleFilter::
decimate_noadjust(short *in,
        int size,
        short   *out)
{
    int i;

    if (size <= 0)
        return (0);
    else if (down <= 1)     // normal filter
        return (Fir::filter_noadjust(in, size, out));
    else if (size <= down_offset) { // just update states
        update_short(in, size);
        down_offset -= size;
        return (0);
    }

    double *in_buf = new double[size];
    short2double(in_buf, in, size);

    // filter and decimate and output
    short   *out_ptr = out;
    int init_size = (size <= order)? size : order;
    for (i = down_offset; i < init_size; i += down)
        *out_ptr++ = double2short(convolve(coef, in_buf, i + 1) +
            convolve(coef + i + 1, state + i, order - i));
    for (; i < size; i += down)
        *out_ptr++ = double2short(convolve(coef, in_buf + i - order,
            order + 1));
    down_offset = i - size;

    updateState(in_buf, size);
    delete in_buf;
    return (out_ptr - out);
}

// decimate with group delay adjusted to 0
int ResampleFilter::
decimate(short  *in,
    int size,
    short   *out)
{
    if (delay <= 0)
        return (decimate_noadjust(in, size, out));
    else if (size <= delay) {
        update_short(in, size);
        delay -= size;
        return (0);
    } else {
        update_short(in, delay);
        in += delay;
        size -= delay;
        delay = 0;
        return (decimate_noadjust(in, size, out));
    }
}

// flush decimate filter
int ResampleFilter::
decimate_flush(short    *out)
{
    int num_in = Fir::getFlushSize();
    short *in = new short[num_in];
    memset(in, 0, num_in * sizeof (short));
    int num_out = decimate_noadjust(in, num_in, out);
    delay += num_in;
    delete in;
    return (num_out);
}

// 1-to-up interpolation
int ResampleFilter::
interpolate_noadjust(short  *in,
            int     size,
            short   *out)
{
    int i, j;

    if (size <= 0)
        return (0);
    else if (up <= 1)           // regular filter
        return (Fir::filter_noadjust(in, size, out));

    double *in_buf = new double[size];
    short2double(in_buf, in, size);
    short *out_ptr = out;
    // befor the 1st input sample, generate  "-up_offset" output samples
    int coef_offset = up + up_offset;
    for (j = up_offset; j < 0; j++) {
        *out_ptr++ = double2short(up * poly_conv(coef + coef_offset,
            order - coef_offset, up, state, num_state));
        coef_offset++;
    }
    // for each of the rest input samples, generate up output samples
    for (i = 1; i < size; i++) {
        for (j = 0; j < up; j++) {
            *out_ptr++ = double2short(up * (poly_conv(coef + j,
                order - j, up, in_buf, i) + poly_conv(
                coef + coef_offset, order - coef_offset, up, state,
                num_state)));
            coef_offset++;
        }
    }

    // for the last input samples, generate "up_offset + up" output samples
    for (j = 0; j < (up_offset + up); j++) {
        *out_ptr++ = double2short(up * (poly_conv(coef + j,
            order - j, up, in_buf, size) + poly_conv(
            coef + coef_offset, order - coef_offset, up, state,
            num_state)));
        coef_offset++;
    }
    updateState(in_buf, size);
    delete in_buf;
    return (out_ptr - out);
}

// flush interpolate filter
int ResampleFilter::
interpolate_flush(short *out)
{
    int num = (Fir::getFlushSize() + up - 1) / up;

    short *in = new short[num];
    memset(in, 0, num * sizeof (short));
    int out_num = interpolate_noadjust(in, num, out);
    delay += num * up;
    delete in;
    return (out_num);
}

// interpolate with delay adjusted
int ResampleFilter::
interpolate(short *in,
        int size,
        short *out)
{
    if (size <= 0)
        return (interpolate_flush(out));
    else if (delay <= 0)
        return (interpolate_noadjust(in, size, out));
    else {
        int delay_in = (delay + up - 1) / up;
        if (size < delay_in)
            delay_in = size;
        double *in_buf = new double[delay_in];
        short2double(in_buf, in, delay_in);
        updateState(in_buf, delay_in);
        delete in_buf;
        delay -= delay_in * up;
        up_offset = delay;
        return (interpolate_noadjust(in + delay_in, size -
            delay_in, out));
    }
}

int ResampleFilter::
filter_noadjust(short   *in,        // non-integer sampling rate conversion
    int size,
    short   *out)
{
    int i, j;

    if (size <= 0)
        return (0);
    else if (up <= 1)
        return (decimate_noadjust(in, size, out));
    else if (down <= 1)
        return (interpolate_noadjust(in, size, out));

    double *in_buf = new double[size];
    short2double(in_buf, in, size);
    short *init_out = out;
    int coef_offset = up_offset + down_offset + up;

    /*
     * before the 1st input sample,
     * start from "up_offset + down_offset"th up-sampled sample
     */
    for (j = up_offset + down_offset; j < 0; j += down) {
        *out++ = double2short(up * poly_conv(coef + coef_offset,
            order - coef_offset, up, state, num_state));
        coef_offset += down;
    }

    // process the input samples until the last one
    for (i = 1; i < size; i++) {
        for (; j < up; j += down) {
            *out++ = double2short(up * (poly_conv(coef + j,
                order - j, up, in_buf, i) + poly_conv(
                coef + coef_offset, order - coef_offset, up, state,
                num_state)));
            coef_offset += down;
        }
        j -= up;
    }

    // for the last input sample, end at the "up + up_offset"th
    for (; j < (up + up_offset); j += down) {
        *out++ = double2short(up * (poly_conv(coef + j, order - j, up,
            in_buf, size) + poly_conv(coef + coef_offset,
            order - coef_offset, up, state, num_state)));
        coef_offset += down;
    }
    down_offset = j - (up + up_offset);

    updateState(in_buf, size);
    delete in_buf;
    return (out - init_out);
}

int ResampleFilter::
getFlushSize(void)
{
    int num_in = (Fir::getFlushSize() + up - 1) / up;
    return ((num_in * up + down - 1 - down_offset) / down);
}

int ResampleFilter::
flush(short *out)       // flush resampling filter

{
    if (down <= 1)
        return (interpolate_flush(out));
    else if (up <= 1)
        return (decimate_flush(out));

    int num = (Fir::getFlushSize() + up - 1) / up;

    short *in = new short[num];
    memset(in, 0, num * sizeof (short));
    int out_num = filter_noadjust(in, num, out);
    delete in;
    delay += num * up;
    return (out_num);
}

/*
 * sampling rate conversion with filter delay adjusted
 */
int ResampleFilter::
filter(
    short   *in,
    int size,
    short   *out)
{
    if (size <= 0)
        return (flush(out));
    else if (up <= 1)
        return (decimate(in, size, out));
    else if (down <= 1)
        return (interpolate(in, size, out));
    else if (delay <= 0)
        return (filter_noadjust(in, size, out));
    else {
        int delay_in = (delay + up - 1) / up;
        if (size < delay_in)
            delay_in = size;
        double *in_buf = new double[delay_in];
        short2double(in_buf, in, delay_in);
        updateState(in_buf, delay_in);
        delete in_buf;
        delay -= up * delay_in;
        if (delay <= 0) {
            up_offset = delay;
            down_offset = 0;
        }
        return (filter_noadjust(in + delay_in, size - delay_in, out));
    }
}