ref: fbed746cb2d0fee57eae090e67d148d89923f6ff
dir: /silk/LPC_fit.c/
/***********************************************************************
Copyright (c) 2013, Koen Vos. All rights reserved.
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modification, are permitted provided that the following conditions
are met:
- Redistributions of source code must retain the above copyright notice,
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names of specific contributors, may be used to endorse or promote
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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***********************************************************************/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "SigProc_FIX.h"
/* Convert int32 coefficients to int16 coefs and make sure there's no wrap-around.
This logic is reused in _celt_lpc(). Any bug fixes should also be applied there. */
void silk_LPC_fit(
opus_int16 *a_QOUT, /* O Output signal */
opus_int32 *a_QIN, /* I/O Input signal */
const opus_int QOUT, /* I Input Q domain */
const opus_int QIN, /* I Input Q domain */
const opus_int d /* I Filter order */
)
{
opus_int i, k, idx = 0;
opus_int32 maxabs, absval, chirp_Q16;
/* Limit the maximum absolute value of the prediction coefficients, so that they'll fit in int16 */
for( i = 0; i < 10; i++ ) {
/* Find maximum absolute value and its index */
maxabs = 0;
for( k = 0; k < d; k++ ) {
absval = silk_abs( a_QIN[k] );
if( absval > maxabs ) {
maxabs = absval;
idx = k;
}
}
maxabs = silk_RSHIFT_ROUND( maxabs, QIN - QOUT );
if( maxabs > silk_int16_MAX ) {
/* Reduce magnitude of prediction coefficients */
maxabs = silk_min( maxabs, 163838 ); /* ( silk_int32_MAX >> 14 ) + silk_int16_MAX = 163838 */
chirp_Q16 = SILK_FIX_CONST( 0.999, 16 ) - silk_DIV32( silk_LSHIFT( maxabs - silk_int16_MAX, 14 ),
silk_RSHIFT32( silk_MUL( maxabs, idx + 1), 2 ) );
silk_bwexpander_32( a_QIN, d, chirp_Q16 );
} else {
break;
}
}
if( i == 10 ) {
/* Reached the last iteration, clip the coefficients */
for( k = 0; k < d; k++ ) {
a_QOUT[ k ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( a_QIN[ k ], QIN - QOUT ) );
a_QIN[ k ] = silk_LSHIFT( (opus_int32)a_QOUT[ k ], QIN - QOUT );
}
} else {
for( k = 0; k < d; k++ ) {
a_QOUT[ k ] = (opus_int16)silk_RSHIFT_ROUND( a_QIN[ k ], QIN - QOUT );
}
}
}