152 lines
6.3 KiB
C
152 lines
6.3 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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/* conversion between prediction filter coefficients and LSFs */
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/* order should be even */
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/* a piecewise linear approximation maps LSF <-> cos(LSF) */
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/* therefore the result is not accurate LSFs, but the two */
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/* function are accurate inverses of each other */
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#include "SKP_Silk_SigProc_FIX.h"
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/* helper function for NLSF2A(..) */
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SKP_INLINE void SKP_Silk_NLSF2A_find_poly(
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SKP_int32 *out, /* o intermediate polynomial, Q20 */
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const SKP_int32 *cLSF, /* i vector of interleaved 2*cos(LSFs), Q20 */
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SKP_int dd /* i polynomial order (= 1/2 * filter order) */
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)
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{
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SKP_int k, n;
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SKP_int32 ftmp;
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out[0] = SKP_LSHIFT( 1, 20 );
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out[1] = -cLSF[0];
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for( k = 1; k < dd; k++ ) {
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ftmp = cLSF[2*k]; // Q20
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out[k+1] = SKP_LSHIFT( out[k-1], 1 ) - (SKP_int32)SKP_RSHIFT_ROUND64( SKP_SMULL( ftmp, out[k] ), 20 );
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for( n = k; n > 1; n-- ) {
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out[n] += out[n-2] - (SKP_int32)SKP_RSHIFT_ROUND64( SKP_SMULL( ftmp, out[n-1] ), 20 );
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}
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out[1] -= ftmp;
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}
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}
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/* compute whitening filter coefficients from normalized line spectral frequencies */
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void SKP_Silk_NLSF2A(
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SKP_int16 *a, /* o monic whitening filter coefficients in Q12, [d] */
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const SKP_int *NLSF, /* i normalized line spectral frequencies in Q15, [d] */
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const SKP_int d /* i filter order (should be even) */
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)
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{
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SKP_int k, i, dd;
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SKP_int32 cos_LSF_Q20[SKP_Silk_MAX_ORDER_LPC];
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SKP_int32 P[SKP_Silk_MAX_ORDER_LPC/2+1], Q[SKP_Silk_MAX_ORDER_LPC/2+1];
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SKP_int32 Ptmp, Qtmp;
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SKP_int32 f_int;
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SKP_int32 f_frac;
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SKP_int32 cos_val, delta;
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SKP_int32 a_int32[SKP_Silk_MAX_ORDER_LPC];
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SKP_int32 maxabs, absval, idx=0, sc_Q16;
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SKP_assert(LSF_COS_TAB_SZ_FIX == 128);
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/* convert LSFs to 2*cos(LSF(i)), using piecewise linear curve from table */
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for( k = 0; k < d; k++ ) {
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SKP_assert(NLSF[k] >= 0 );
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SKP_assert(NLSF[k] <= 32767 );
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/* f_int on a scale 0-127 (rounded down) */
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f_int = SKP_RSHIFT( NLSF[k], 15 - 7 );
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/* f_frac, range: 0..255 */
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f_frac = NLSF[k] - SKP_LSHIFT( f_int, 15 - 7 );
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SKP_assert(f_int >= 0);
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SKP_assert(f_int < LSF_COS_TAB_SZ_FIX );
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/* Read start and end value from table */
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cos_val = SKP_Silk_LSFCosTab_FIX_Q12[ f_int ]; /* Q12 */
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delta = SKP_Silk_LSFCosTab_FIX_Q12[ f_int + 1 ] - cos_val; /* Q12, with a range of 0..200 */
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/* Linear interpolation */
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cos_LSF_Q20[k] = SKP_LSHIFT( cos_val, 8 ) + SKP_MUL( delta, f_frac ); /* Q20 */
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}
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dd = SKP_RSHIFT( d, 1 );
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/* generate even and odd polynomials using convolution */
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SKP_Silk_NLSF2A_find_poly( P, &cos_LSF_Q20[0], dd );
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SKP_Silk_NLSF2A_find_poly( Q, &cos_LSF_Q20[1], dd );
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/* convert even and odd polynomials to SKP_int32 Q12 filter coefs */
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for( k = 0; k < dd; k++ ) {
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Ptmp = P[k+1] + P[k];
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Qtmp = Q[k+1] - Q[k];
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/* the Ptmp and Qtmp values at this stage need to fit in int32 */
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a_int32[k] = -SKP_RSHIFT_ROUND( Ptmp + Qtmp, 9 ); /* Q20 -> Q12 */
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a_int32[d-k-1] = SKP_RSHIFT_ROUND( Qtmp - Ptmp, 9 ); /* Q20 -> Q12 */
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}
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/* Limit the maximum absolute value of the prediction coefficients */
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for( i = 0; i < 10; i++ ) {
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/* Find maximum absolute value and its index */
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maxabs = 0;
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for( k = 0; k < d; k++ ) {
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absval = SKP_abs( a_int32[k] );
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if( absval > maxabs ) {
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maxabs = absval;
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idx = k;
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}
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}
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if( maxabs > SKP_int16_MAX ) {
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/* Reduce magnitude of prediction coefficients */
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maxabs = SKP_min( maxabs, 98369 ); // ( SKP_int32_MAX / ( 65470 >> 2 ) ) + SKP_int16_MAX = 98369
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sc_Q16 = 65470 - SKP_DIV32( SKP_MUL( 65470 >> 2, maxabs - SKP_int16_MAX ),
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SKP_RSHIFT32( SKP_MUL( maxabs, idx + 1), 2 ) );
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SKP_Silk_bwexpander_32( a_int32, d, sc_Q16 );
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} else {
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break;
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}
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}
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/* Reached the last iteration */
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if( i == 10 ) {
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SKP_assert(0);
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for( k = 0; k < d; k++ ) {
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a_int32[k] = SKP_SAT16( a_int32[k] );
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}
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}
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/* Return as SKP_int16 Q12 coefficients */
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for( k = 0; k < d; k++ ) {
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a[k] = (SKP_int16)a_int32[k];
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}
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}
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