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/*
* 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
for (i = (len >> 1); i > 0; i--)
{
// lower allpass filter
in32 = (WebRtc_Word32)(*inptr++) << 10;
diff = in32 - state[1];
tmp1 = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass2[0], diff, state[0] );
state[0] = in32;
diff = tmp1 - state[2];
tmp2 = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass2[1], diff, state[1] );
state[1] = tmp1;
diff = tmp2 - state[3];
state[3] = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass2[2], diff, state[2] );
state[2] = tmp2;
// upper allpass filter
in32 = (WebRtc_Word32)(*inptr++) << 10;
diff = in32 - state[5];
tmp1 = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass1[0], diff, state[4] );
state[4] = in32;
diff = tmp1 - state[6];
tmp2 = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass1[1], diff, state[5] );
state[5] = tmp1;
diff = tmp2 - state[7];
state[7] = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass1[2], diff, state[6] );
state[6] = tmp2;
// add two allpass outputs, divide by two and round
out32 = (state[3] + state[7] + 1024) >> 11;
// limit amplitude to prevent wrap-around, and write to output array
if (out32 > 32767)
*outptr++ = 32767;
else if (out32 < -32768)
*outptr++ = -32768;
else
*outptr++ = (WebRtc_Word16)out32;
}
}
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
for (i = len; i > 0; i--)
{
// lower allpass filter
in32 = (WebRtc_Word32)(*inptr++) << 10;
diff = in32 - state[1];
tmp1 = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass1[0], diff, state[0] );
state[0] = in32;
diff = tmp1 - state[2];
tmp2 = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass1[1], diff, state[1] );
state[1] = tmp1;
diff = tmp2 - state[3];
state[3] = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass1[2], diff, state[2] );
state[2] = tmp2;
// round; limit amplitude to prevent wrap-around; write to output array
out32 = (state[3] + 512) >> 10;
if (out32 > 32767)
*outptr++ = 32767;
else if (out32 < -32768)
*outptr++ = -32768;
else
*outptr++ = (WebRtc_Word16)out32;
// upper allpass filter
diff = in32 - state[5];
tmp1 = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass2[0], diff, state[4] );
state[4] = in32;
diff = tmp1 - state[6];
tmp2 = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass2[1], diff, state[5] );
state[5] = tmp1;
diff = tmp2 - state[7];
state[7] = WEBRTC_SPL_SCALEDIFF32( kResampleAllpass2[2], diff, state[6] );
state[6] = tmp2;
// round; limit amplitude to prevent wrap-around; write to output array
out32 = (state[7] + 512) >> 10;
if (out32 > 32767)
*outptr++ = 32767;
else if (out32 < -32768)
*outptr++ = -32768;
else
*outptr++ = (WebRtc_Word16)out32;
}
}
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