92 lines
4.4 KiB
C
92 lines
4.4 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_schur.c *
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* *
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* Calculates the reflection coefficients from the correlation sequence *
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* *
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* Copyright 2008 (c), Skype Limited *
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* Date: 080103 *
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* */
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#include "SKP_Silk_SigProc_FIX.h"
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/* Faster than schur64(), but much less accurate. */
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/* uses SMLAWB(), requiring armv5E and higher. */
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void SKP_Silk_schur(
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SKP_int16 *rc_Q15, /* O: reflection coefficients [order] Q15 */
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const SKP_int32 *c, /* I: correlations [order+1] */
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const SKP_int32 order /* I: prediction order */
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)
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{
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SKP_int k, n, lz;
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SKP_int32 C[ SigProc_MAX_ORDER_LPC + 1 ][ 2 ];
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SKP_int32 Ctmp1, Ctmp2, rc_tmp_Q15;
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/* Get number of leading zeros */
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lz = SKP_Silk_CLZ32( c[ 0 ] );
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/* Copy correlations and adjust level to Q30 */
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if( lz < 2 ) {
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/* lz must be 1, so shift one to the right */
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for( k = 0; k < order + 1; k++ ) {
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C[ k ][ 0 ] = C[ k ][ 1 ] = SKP_RSHIFT( c[ k ], 1 );
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}
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} else if( lz > 2 ) {
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/* Shift to the left */
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lz -= 2;
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for( k = 0; k < order + 1; k++ ) {
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C[ k ][ 0 ] = C[ k ][ 1 ] = SKP_LSHIFT( c[k], lz );
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}
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} else {
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/* No need to shift */
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for( k = 0; k < order + 1; k++ ) {
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C[ k ][ 0 ] = C[ k ][ 1 ] = c[ k ];
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}
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}
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for( k = 0; k < order; k++ ) {
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/* Get reflection coefficient */
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rc_tmp_Q15 = -SKP_DIV32_16( C[ k + 1 ][ 0 ], SKP_max_32( SKP_RSHIFT( C[ 0 ][ 1 ], 15 ), 1 ) );
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/* Clip (shouldn't happen for properly conditioned inputs) */
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rc_tmp_Q15 = SKP_SAT16( rc_tmp_Q15 );
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/* Store */
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rc_Q15[ k ] = (SKP_int16)rc_tmp_Q15;
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/* Update correlations */
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for( n = 0; n < order - k; n++ ) {
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Ctmp1 = C[ n + k + 1 ][ 0 ];
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Ctmp2 = C[ n ][ 1 ];
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C[ n + k + 1 ][ 0 ] = SKP_SMLAWB( Ctmp1, SKP_LSHIFT( Ctmp2, 1 ), rc_tmp_Q15 );
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C[ n ][ 1 ] = SKP_SMLAWB( Ctmp2, SKP_LSHIFT( Ctmp1, 1 ), rc_tmp_Q15 );
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}
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}
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}
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