70 lines
3.9 KiB
C
70 lines
3.9 KiB
C
/***********************************************************************
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Copyright (c) 2006-2010, 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_allpass_int.c *
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* *
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* First-order allpass filter with *
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* transfer function: *
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* *
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* A + Z^(-1) *
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* H(z) = ------------ *
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* 1 + A*Z^(-1) *
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* *
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* Implemented using minimum multiplier filter design. *
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* *
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* Reference: http://www.univ.trieste.it/~ramponi/teaching/ *
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* DSP/materiale/Ch6(2).pdf *
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* *
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* Copyright 2007 (c), Skype Limited *
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* Date: 070525 *
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* */
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#include "SKP_Silk_SigProc_FIX.h"
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/* First-order allpass filter */
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void SKP_Silk_allpass_int(
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const SKP_int32 *in, /* I: Q25 input signal [len] */
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SKP_int32 *S, /* I/O: Q25 state [1] */
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SKP_int A, /* I: Q15 coefficient (0 <= A < 32768) */
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SKP_int32 *out, /* O: Q25 output signal [len] */
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const SKP_int32 len /* I: Number of samples */
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)
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{
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SKP_int32 Y2, X2, S0;
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SKP_int k;
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S0 = S[ 0 ];
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for( k = len - 1; k >= 0; k-- ) {
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Y2 = *in - S0;
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X2 = ( Y2 >> 15 ) * A + ( ( ( Y2 & 0x00007FFF ) * A ) >> 15 );
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( *out++ ) = S0 + X2;
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S0 = ( *in++ ) + X2;
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}
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S[ 0 ] = S0;
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}
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