src/common_audio/signal_processing_library/main/source/resample_by_2.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 file contains the resampling by two functions.
 * The description header can be found in signal_processing_library.h
 *
 */

#include "signal_processing_library.h"

// allpass filter coefficients.
static const WebRtc_UWord16 kResampleAllpass1[3] = {3284, 24441, 49528};
static const WebRtc_UWord16 kResampleAllpass2[3] = {12199, 37471, 60255};

// decimator
void WebRtcSpl_DownsampleBy2(const WebRtc_Word16* in, const WebRtc_Word16 len,
                             WebRtc_Word16* out, WebRtc_Word32* filtState)
{
    const WebRtc_Word16 *inptr;
    WebRtc_Word16 *outptr;
    WebRtc_Word32 *state;
    WebRtc_Word32 tmp1, tmp2, diff, in32, out32;
    WebRtc_Word16 i;

    // local versions of pointers to input and output arrays
    inptr = in; // input array
    outptr = out; // output array (of length len/2)
    state = filtState; // filter state array; length = 8

    register WebRtc_Word32 state0 = state[0];
    register WebRtc_Word32 state1 = state[1];
    register WebRtc_Word32 state2 = state[2];
    register WebRtc_Word32 state3 = state[3];
    register WebRtc_Word32 state4 = state[4];
    register WebRtc_Word32 state5 = state[5];
    register WebRtc_Word32 state6 = state[6];
    register WebRtc_Word32 state7 = state[7];

    for (i = (len >> 1); i > 0; i--)
    {
        // lower allpass filter
        in32 = (WebRtc_Word32)(*inptr++) << 10;
        diff = in32 - state1;
        tmp1 = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass2[0], diff, state0 );
        state0 = in32;
        diff = tmp1 - state2;
        tmp2 = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass2[1], diff, state1 );
        state1 = tmp1;
        diff = tmp2 - state3;
        state3 = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass2[2], diff, state2 );
        state2 = tmp2;

        // upper allpass filter
        in32 = (WebRtc_Word32)(*inptr++) << 10;
        diff = in32 - state5;
        tmp1 = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass1[0], diff, state4 );
        state4 = in32;
        diff = tmp1 - state6;
        tmp2 = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass1[1], diff, state5 );
        state5 = tmp1;
        diff = tmp2 - state7;
        state7 = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass1[2], diff, state6 );
        state6 = tmp2;

        // add two allpass outputs, divide by two and round
        out32 = (state3 + state7 + 1024) >> 11;

        // limit amplitude to prevent wrap-around, and write to output array
#ifdef WEBRTC_ARCH_ARM_V7A
        __asm__("ssat %r0, #16, %r1" : "=r"(*outptr) : "r"(out32));
        outptr++;
#else
        if (out32 > 32767)
            *outptr++ = 32767;
        else if (out32 < -32768)
            *outptr++ = -32768;
        else
            *outptr++ = (WebRtc_Word16)out32;
#endif
    }

    state[0]=state0;
    state[1]=state1;
    state[2]=state2;
    state[3]=state3;
    state[4]=state4;
    state[5]=state5;
    state[6]=state6;
    state[7]=state7;
}

void WebRtcSpl_UpsampleBy2(const WebRtc_Word16* in, WebRtc_Word16 len, WebRtc_Word16* out,
                           WebRtc_Word32* filtState)
{
    const WebRtc_Word16 *inptr;
    WebRtc_Word16 *outptr;
    WebRtc_Word32 *state;
    WebRtc_Word32 tmp1, tmp2, diff, in32, out32;
    WebRtc_Word16 i;

    // local versions of pointers to input and output arrays
    inptr = in; // input array
    outptr = out; // output array (of length len*2)
    state = filtState; // filter state array; length = 8

    register WebRtc_Word32 state0 = state[0];
    register WebRtc_Word32 state1 = state[1];
    register WebRtc_Word32 state2 = state[2];
    register WebRtc_Word32 state3 = state[3];
    register WebRtc_Word32 state4 = state[4];
    register WebRtc_Word32 state5 = state[5];
    register WebRtc_Word32 state6 = state[6];
    register WebRtc_Word32 state7 = state[7];

    for (i = len; i > 0; i--)
    {
        // lower allpass filter
        in32 = (WebRtc_Word32)(*inptr++) << 10;
        diff = in32 - state1;
        tmp1 = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass1[0], diff, state0 );
        state0 = in32;
        diff = tmp1 - state2;
        tmp2 = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass1[1], diff, state1 );
        state1 = tmp1;
        diff = tmp2 - state3;
        state3 = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass1[2], diff, state2 );
        state2 = tmp2;

        // round; limit amplitude to prevent wrap-around; write to output array
        out32 = (state3 + 512) >> 10;
#ifdef WEBRTC_ARCH_ARM_V7A
        __asm__("ssat %r0, #16, %r1":"=r"(*outptr): "r"(out32));
        outptr++;
#else
        if (out32 > 32767)
            *outptr++ = 32767;
        else if (out32 < -32768)
            *outptr++ = -32768;
        else
            *outptr++ = (WebRtc_Word16)out32;
#endif

        // upper allpass filter
        diff = in32 - state5;
        tmp1 = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass2[0], diff, state4 );
        state4 = in32;
        diff = tmp1 - state6;
        tmp2 = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass2[1], diff, state5 );
        state5 = tmp1;
        diff = tmp2 - state7;
        state7 = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass2[2], diff, state6 );
        state6 = tmp2;

        // round; limit amplitude to prevent wrap-around; write to output array
        out32 = (state7 + 512) >> 10;
#ifdef WEBRTC_ARCH_ARM_V7A
        __asm__("ssat %r0, #16, %r1":"=r"(*outptr): "r"(out32));
        outptr++;
#else
        if (out32 > 32767)
            *outptr++ = 32767;
        else if (out32 < -32768)
            *outptr++ = -32768;
        else
            *outptr++ = (WebRtc_Word16)out32;
#endif
    }
    state[0]=state0;
    state[1]=state1;
    state[2]=state2;
    state[3]=state3;
    state[4]=state4;
    state[5]=state5;
    state[6]=state6;
    state[7]=state7;

}