common_audio/signal_processing/resample_by_2_internal.c

/*
 *  Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */


/*
 * This header file contains some internal resampling functions.
 *
 */

#include "webrtc/common_audio/signal_processing/resample_by_2_internal.h"

// allpass filter coefficients.
static const int16_t kResampleAllpass[2][3] = {
        {821, 6110, 12382},
        {3050, 9368, 15063}
};

//
//   decimator
// input:  int32_t (shifted 15 positions to the left, + offset 16384) OVERWRITTEN!
// output: int16_t (saturated) (of length len/2)
// state:  filter state array; length = 8

void WebRtcSpl_DownBy2IntToShort(int32_t *in, int32_t len, int16_t *out,
                                 int32_t *state)
{
    int32_t tmp0, tmp1, diff;
    int32_t i;

    len >>= 1;

    // lower allpass filter (operates on even input samples)
    for (i = 0; i < len; i++)
    {
        tmp0 = in[i << 1];
        diff = tmp0 - state[1];
        // scale down and round
        diff = (diff + (1 << 13)) >> 14;
        tmp1 = state[0] + diff * kResampleAllpass[1][0];
        state[0] = tmp0;
        diff = tmp1 - state[2];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        tmp0 = state[1] + diff * kResampleAllpass[1][1];
        state[1] = tmp1;
        diff = tmp0 - state[3];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        state[3] = state[2] + diff * kResampleAllpass[1][2];
        state[2] = tmp0;

        // divide by two and store temporarily
        in[i << 1] = (state[3] >> 1);
    }

    in++;

    // upper allpass filter (operates on odd input samples)
    for (i = 0; i < len; i++)
    {
        tmp0 = in[i << 1];
        diff = tmp0 - state[5];
        // scale down and round
        diff = (diff + (1 << 13)) >> 14;
        tmp1 = state[4] + diff * kResampleAllpass[0][0];
        state[4] = tmp0;
        diff = tmp1 - state[6];
        // scale down and round
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        tmp0 = state[5] + diff * kResampleAllpass[0][1];
        state[5] = tmp1;
        diff = tmp0 - state[7];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        state[7] = state[6] + diff * kResampleAllpass[0][2];
        state[6] = tmp0;

        // divide by two and store temporarily
        in[i << 1] = (state[7] >> 1);
    }

    in--;

    // combine allpass outputs
    for (i = 0; i < len; i += 2)
    {
        // divide by two, add both allpass outputs and round
        tmp0 = (in[i << 1] + in[(i << 1) + 1]) >> 15;
        tmp1 = (in[(i << 1) + 2] + in[(i << 1) + 3]) >> 15;
        if (tmp0 > (int32_t)0x00007FFF)
            tmp0 = 0x00007FFF;
        if (tmp0 < (int32_t)0xFFFF8000)
            tmp0 = 0xFFFF8000;
        out[i] = (int16_t)tmp0;
        if (tmp1 > (int32_t)0x00007FFF)
            tmp1 = 0x00007FFF;
        if (tmp1 < (int32_t)0xFFFF8000)
            tmp1 = 0xFFFF8000;
        out[i + 1] = (int16_t)tmp1;
    }
}

//
//   decimator
// input:  int16_t
// output: int32_t (shifted 15 positions to the left, + offset 16384) (of length len/2)
// state:  filter state array; length = 8

void WebRtcSpl_DownBy2ShortToInt(const int16_t *in,
                                  int32_t len,
                                  int32_t *out,
                                  int32_t *state)
{
    int32_t tmp0, tmp1, diff;
    int32_t i;

    len >>= 1;

    // lower allpass filter (operates on even input samples)
    for (i = 0; i < len; i++)
    {
        tmp0 = ((int32_t)in[i << 1] << 15) + (1 << 14);
        diff = tmp0 - state[1];
        // scale down and round
        diff = (diff + (1 << 13)) >> 14;
        tmp1 = state[0] + diff * kResampleAllpass[1][0];
        state[0] = tmp0;
        diff = tmp1 - state[2];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        tmp0 = state[1] + diff * kResampleAllpass[1][1];
        state[1] = tmp1;
        diff = tmp0 - state[3];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        state[3] = state[2] + diff * kResampleAllpass[1][2];
        state[2] = tmp0;

        // divide by two and store temporarily
        out[i] = (state[3] >> 1);
    }

    in++;

    // upper allpass filter (operates on odd input samples)
    for (i = 0; i < len; i++)
    {
        tmp0 = ((int32_t)in[i << 1] << 15) + (1 << 14);
        diff = tmp0 - state[5];
        // scale down and round
        diff = (diff + (1 << 13)) >> 14;
        tmp1 = state[4] + diff * kResampleAllpass[0][0];
        state[4] = tmp0;
        diff = tmp1 - state[6];
        // scale down and round
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        tmp0 = state[5] + diff * kResampleAllpass[0][1];
        state[5] = tmp1;
        diff = tmp0 - state[7];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        state[7] = state[6] + diff * kResampleAllpass[0][2];
        state[6] = tmp0;

        // divide by two and store temporarily
        out[i] += (state[7] >> 1);
    }

    in--;
}

//
//   interpolator
// input:  int16_t
// output: int32_t (normalized, not saturated) (of length len*2)
// state:  filter state array; length = 8
void WebRtcSpl_UpBy2ShortToInt(const int16_t *in, int32_t len, int32_t *out,
                               int32_t *state)
{
    int32_t tmp0, tmp1, diff;
    int32_t i;

    // upper allpass filter (generates odd output samples)
    for (i = 0; i < len; i++)
    {
        tmp0 = ((int32_t)in[i] << 15) + (1 << 14);
        diff = tmp0 - state[5];
        // scale down and round
        diff = (diff + (1 << 13)) >> 14;
        tmp1 = state[4] + diff * kResampleAllpass[0][0];
        state[4] = tmp0;
        diff = tmp1 - state[6];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        tmp0 = state[5] + diff * kResampleAllpass[0][1];
        state[5] = tmp1;
        diff = tmp0 - state[7];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        state[7] = state[6] + diff * kResampleAllpass[0][2];
        state[6] = tmp0;

        // scale down, round and store
        out[i << 1] = state[7] >> 15;
    }

    out++;

    // lower allpass filter (generates even output samples)
    for (i = 0; i < len; i++)
    {
        tmp0 = ((int32_t)in[i] << 15) + (1 << 14);
        diff = tmp0 - state[1];
        // scale down and round
        diff = (diff + (1 << 13)) >> 14;
        tmp1 = state[0] + diff * kResampleAllpass[1][0];
        state[0] = tmp0;
        diff = tmp1 - state[2];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        tmp0 = state[1] + diff * kResampleAllpass[1][1];
        state[1] = tmp1;
        diff = tmp0 - state[3];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        state[3] = state[2] + diff * kResampleAllpass[1][2];
        state[2] = tmp0;

        // scale down, round and store
        out[i << 1] = state[3] >> 15;
    }
}

//
//   interpolator
// input:  int32_t (shifted 15 positions to the left, + offset 16384)
// output: int32_t (shifted 15 positions to the left, + offset 16384) (of length len*2)
// state:  filter state array; length = 8
void WebRtcSpl_UpBy2IntToInt(const int32_t *in, int32_t len, int32_t *out,
                             int32_t *state)
{
    int32_t tmp0, tmp1, diff;
    int32_t i;

    // upper allpass filter (generates odd output samples)
    for (i = 0; i < len; i++)
    {
        tmp0 = in[i];
        diff = tmp0 - state[5];
        // scale down and round
        diff = (diff + (1 << 13)) >> 14;
        tmp1 = state[4] + diff * kResampleAllpass[0][0];
        state[4] = tmp0;
        diff = tmp1 - state[6];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        tmp0 = state[5] + diff * kResampleAllpass[0][1];
        state[5] = tmp1;
        diff = tmp0 - state[7];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        state[7] = state[6] + diff * kResampleAllpass[0][2];
        state[6] = tmp0;

        // scale down, round and store
        out[i << 1] = state[7];
    }

    out++;

    // lower allpass filter (generates even output samples)
    for (i = 0; i < len; i++)
    {
        tmp0 = in[i];
        diff = tmp0 - state[1];
        // scale down and round
        diff = (diff + (1 << 13)) >> 14;
        tmp1 = state[0] + diff * kResampleAllpass[1][0];
        state[0] = tmp0;
        diff = tmp1 - state[2];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        tmp0 = state[1] + diff * kResampleAllpass[1][1];
        state[1] = tmp1;
        diff = tmp0 - state[3];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        state[3] = state[2] + diff * kResampleAllpass[1][2];
        state[2] = tmp0;

        // scale down, round and store
        out[i << 1] = state[3];
    }
}

//
//   interpolator
// input:  int32_t (shifted 15 positions to the left, + offset 16384)
// output: int16_t (saturated) (of length len*2)
// state:  filter state array; length = 8
void WebRtcSpl_UpBy2IntToShort(const int32_t *in, int32_t len, int16_t *out,
                               int32_t *state)
{
    int32_t tmp0, tmp1, diff;
    int32_t i;

    // upper allpass filter (generates odd output samples)
    for (i = 0; i < len; i++)
    {
        tmp0 = in[i];
        diff = tmp0 - state[5];
        // scale down and round
        diff = (diff + (1 << 13)) >> 14;
        tmp1 = state[4] + diff * kResampleAllpass[0][0];
        state[4] = tmp0;
        diff = tmp1 - state[6];
        // scale down and round
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        tmp0 = state[5] + diff * kResampleAllpass[0][1];
        state[5] = tmp1;
        diff = tmp0 - state[7];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        state[7] = state[6] + diff * kResampleAllpass[0][2];
        state[6] = tmp0;

        // scale down, saturate and store
        tmp1 = state[7] >> 15;
        if (tmp1 > (int32_t)0x00007FFF)
            tmp1 = 0x00007FFF;
        if (tmp1 < (int32_t)0xFFFF8000)
            tmp1 = 0xFFFF8000;
        out[i << 1] = (int16_t)tmp1;
    }

    out++;

    // lower allpass filter (generates even output samples)
    for (i = 0; i < len; i++)
    {
        tmp0 = in[i];
        diff = tmp0 - state[1];
        // scale down and round
        diff = (diff + (1 << 13)) >> 14;
        tmp1 = state[0] + diff * kResampleAllpass[1][0];
        state[0] = tmp0;
        diff = tmp1 - state[2];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        tmp0 = state[1] + diff * kResampleAllpass[1][1];
        state[1] = tmp1;
        diff = tmp0 - state[3];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        state[3] = state[2] + diff * kResampleAllpass[1][2];
        state[2] = tmp0;

        // scale down, saturate and store
        tmp1 = state[3] >> 15;
        if (tmp1 > (int32_t)0x00007FFF)
            tmp1 = 0x00007FFF;
        if (tmp1 < (int32_t)0xFFFF8000)
            tmp1 = 0xFFFF8000;
        out[i << 1] = (int16_t)tmp1;
    }
}

//   lowpass filter
// input:  int16_t
// output: int32_t (normalized, not saturated)
// state:  filter state array; length = 8
void WebRtcSpl_LPBy2ShortToInt(const int16_t* in, int32_t len, int32_t* out,
                               int32_t* state)
{
    int32_t tmp0, tmp1, diff;
    int32_t i;

    len >>= 1;

    // lower allpass filter: odd input -> even output samples
    in++;
    // initial state of polyphase delay element
    tmp0 = state[12];
    for (i = 0; i < len; i++)
    {
        diff = tmp0 - state[1];
        // scale down and round
        diff = (diff + (1 << 13)) >> 14;
        tmp1 = state[0] + diff * kResampleAllpass[1][0];
        state[0] = tmp0;
        diff = tmp1 - state[2];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        tmp0 = state[1] + diff * kResampleAllpass[1][1];
        state[1] = tmp1;
        diff = tmp0 - state[3];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        state[3] = state[2] + diff * kResampleAllpass[1][2];
        state[2] = tmp0;

        // scale down, round and store
        out[i << 1] = state[3] >> 1;
        tmp0 = ((int32_t)in[i << 1] << 15) + (1 << 14);
    }
    in--;

    // upper allpass filter: even input -> even output samples
    for (i = 0; i < len; i++)
    {
        tmp0 = ((int32_t)in[i << 1] << 15) + (1 << 14);
        diff = tmp0 - state[5];
        // scale down and round
        diff = (diff + (1 << 13)) >> 14;
        tmp1 = state[4] + diff * kResampleAllpass[0][0];
        state[4] = tmp0;
        diff = tmp1 - state[6];
        // scale down and round
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        tmp0 = state[5] + diff * kResampleAllpass[0][1];
        state[5] = tmp1;
        diff = tmp0 - state[7];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        state[7] = state[6] + diff * kResampleAllpass[0][2];
        state[6] = tmp0;

        // average the two allpass outputs, scale down and store
        out[i << 1] = (out[i << 1] + (state[7] >> 1)) >> 15;
    }

    // switch to odd output samples
    out++;

    // lower allpass filter: even input -> odd output samples
    for (i = 0; i < len; i++)
    {
        tmp0 = ((int32_t)in[i << 1] << 15) + (1 << 14);
        diff = tmp0 - state[9];
        // scale down and round
        diff = (diff + (1 << 13)) >> 14;
        tmp1 = state[8] + diff * kResampleAllpass[1][0];
        state[8] = tmp0;
        diff = tmp1 - state[10];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        tmp0 = state[9] + diff * kResampleAllpass[1][1];
        state[9] = tmp1;
        diff = tmp0 - state[11];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        state[11] = state[10] + diff * kResampleAllpass[1][2];
        state[10] = tmp0;

        // scale down, round and store
        out[i << 1] = state[11] >> 1;
    }

    // upper allpass filter: odd input -> odd output samples
    in++;
    for (i = 0; i < len; i++)
    {
        tmp0 = ((int32_t)in[i << 1] << 15) + (1 << 14);
        diff = tmp0 - state[13];
        // scale down and round
        diff = (diff + (1 << 13)) >> 14;
        tmp1 = state[12] + diff * kResampleAllpass[0][0];
        state[12] = tmp0;
        diff = tmp1 - state[14];
        // scale down and round
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        tmp0 = state[13] + diff * kResampleAllpass[0][1];
        state[13] = tmp1;
        diff = tmp0 - state[15];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        state[15] = state[14] + diff * kResampleAllpass[0][2];
        state[14] = tmp0;

        // average the two allpass outputs, scale down and store
        out[i << 1] = (out[i << 1] + (state[15] >> 1)) >> 15;
    }
}

//   lowpass filter
// input:  int32_t (shifted 15 positions to the left, + offset 16384)
// output: int32_t (normalized, not saturated)
// state:  filter state array; length = 8
void WebRtcSpl_LPBy2IntToInt(const int32_t* in, int32_t len, int32_t* out,
                             int32_t* state)
{
    int32_t tmp0, tmp1, diff;
    int32_t i;

    len >>= 1;

    // lower allpass filter: odd input -> even output samples
    in++;
    // initial state of polyphase delay element
    tmp0 = state[12];
    for (i = 0; i < len; i++)
    {
        diff = tmp0 - state[1];
        // scale down and round
        diff = (diff + (1 << 13)) >> 14;
        tmp1 = state[0] + diff * kResampleAllpass[1][0];
        state[0] = tmp0;
        diff = tmp1 - state[2];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        tmp0 = state[1] + diff * kResampleAllpass[1][1];
        state[1] = tmp1;
        diff = tmp0 - state[3];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        state[3] = state[2] + diff * kResampleAllpass[1][2];
        state[2] = tmp0;

        // scale down, round and store
        out[i << 1] = state[3] >> 1;
        tmp0 = in[i << 1];
    }
    in--;

    // upper allpass filter: even input -> even output samples
    for (i = 0; i < len; i++)
    {
        tmp0 = in[i << 1];
        diff = tmp0 - state[5];
        // scale down and round
        diff = (diff + (1 << 13)) >> 14;
        tmp1 = state[4] + diff * kResampleAllpass[0][0];
        state[4] = tmp0;
        diff = tmp1 - state[6];
        // scale down and round
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        tmp0 = state[5] + diff * kResampleAllpass[0][1];
        state[5] = tmp1;
        diff = tmp0 - state[7];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        state[7] = state[6] + diff * kResampleAllpass[0][2];
        state[6] = tmp0;

        // average the two allpass outputs, scale down and store
        out[i << 1] = (out[i << 1] + (state[7] >> 1)) >> 15;
    }

    // switch to odd output samples
    out++;

    // lower allpass filter: even input -> odd output samples
    for (i = 0; i < len; i++)
    {
        tmp0 = in[i << 1];
        diff = tmp0 - state[9];
        // scale down and round
        diff = (diff + (1 << 13)) >> 14;
        tmp1 = state[8] + diff * kResampleAllpass[1][0];
        state[8] = tmp0;
        diff = tmp1 - state[10];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        tmp0 = state[9] + diff * kResampleAllpass[1][1];
        state[9] = tmp1;
        diff = tmp0 - state[11];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        state[11] = state[10] + diff * kResampleAllpass[1][2];
        state[10] = tmp0;

        // scale down, round and store
        out[i << 1] = state[11] >> 1;
    }

    // upper allpass filter: odd input -> odd output samples
    in++;
    for (i = 0; i < len; i++)
    {
        tmp0 = in[i << 1];
        diff = tmp0 - state[13];
        // scale down and round
        diff = (diff + (1 << 13)) >> 14;
        tmp1 = state[12] + diff * kResampleAllpass[0][0];
        state[12] = tmp0;
        diff = tmp1 - state[14];
        // scale down and round
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        tmp0 = state[13] + diff * kResampleAllpass[0][1];
        state[13] = tmp1;
        diff = tmp0 - state[15];
        // scale down and truncate
        diff = diff >> 14;
        if (diff < 0)
            diff += 1;
        state[15] = state[14] + diff * kResampleAllpass[0][2];
        state[14] = tmp0;

        // average the two allpass outputs, scale down and store
        out[i << 1] = (out[i << 1] + (state[15] >> 1)) >> 15;
    }
}