78 lines
4.2 KiB
C
78 lines
4.2 KiB
C
/***********************************************************************
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Copyright (c) 2006-2011, Skype Limited. All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, (subject to the limitations in the disclaimer below)
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are permitted provided that the following conditions are met:
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- Redistributions of source code must retain the above copyright notice,
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this list of conditions and the following disclaimer.
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- Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in the
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documentation and/or other materials provided with the distribution.
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- Neither the name of Skype Limited, nor the names of specific
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contributors, may be used to endorse or promote products derived from
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this software without specific prior written permission.
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NO EXPRESS OR IMPLIED LICENSES TO ANY PARTY'S PATENT RIGHTS ARE GRANTED
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BY THIS LICENSE. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
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CONTRIBUTORS ''AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING,
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BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
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FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
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ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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***********************************************************************/
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/* *
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* SKP_Silk_resampler_private_down4.c *
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* *
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* Downsample by a factor 4 *
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* *
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* Copyright 2010 (c), Skype Limited *
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* */
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#include "SKP_Silk_SigProc_FIX.h"
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#include "SKP_Silk_resampler_private.h"
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/* Downsample by a factor 4. Note: very low quality, only use with input sampling rates above 96 kHz. */
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void SKP_Silk_resampler_private_down4(
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SKP_int32 *S, /* I/O: State vector [ 2 ] */
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SKP_int16 *out, /* O: Output signal [ floor(len/2) ] */
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const SKP_int16 *in, /* I: Input signal [ len ] */
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SKP_int32 inLen /* I: Number of input samples */
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)
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{
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SKP_int32 k, len4 = SKP_RSHIFT32( inLen, 2 );
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SKP_int32 in32, out32, Y, X;
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SKP_assert( SKP_Silk_resampler_down2_0 > 0 );
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SKP_assert( SKP_Silk_resampler_down2_1 < 0 );
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/* Internal variables and state are in Q10 format */
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for( k = 0; k < len4; k++ ) {
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/* Add two input samples and convert to Q10 */
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in32 = SKP_LSHIFT( SKP_ADD32( (SKP_int32)in[ 4 * k ], (SKP_int32)in[ 4 * k + 1 ] ), 9 );
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/* All-pass section for even input sample */
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Y = SKP_SUB32( in32, S[ 0 ] );
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X = SKP_SMLAWB( Y, Y, SKP_Silk_resampler_down2_1 );
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out32 = SKP_ADD32( S[ 0 ], X );
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S[ 0 ] = SKP_ADD32( in32, X );
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/* Add two input samples and convert to Q10 */
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in32 = SKP_LSHIFT( SKP_ADD32( (SKP_int32)in[ 4 * k + 2 ], (SKP_int32)in[ 4 * k + 3 ] ), 9 );
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/* All-pass section for odd input sample */
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Y = SKP_SUB32( in32, S[ 1 ] );
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X = SKP_SMULWB( Y, SKP_Silk_resampler_down2_0 );
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out32 = SKP_ADD32( out32, S[ 1 ] );
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out32 = SKP_ADD32( out32, X );
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S[ 1 ] = SKP_ADD32( in32, X );
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/* Add, convert back to int16 and store to output */
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out[ k ] = (SKP_int16)SKP_SAT16( SKP_RSHIFT_ROUND( out32, 11 ) );
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}
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}
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