253 lines
10 KiB
C
253 lines
10 KiB
C
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/***********************************************************************
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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, are permitted provided that the following conditions
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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 Internet Society, IETF or IETF Trust, nor the
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names of specific contributors, may be used to endorse or promote
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products derived from this software without specific prior written
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permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “AS IS”
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AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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POSSIBILITY OF SUCH DAMAGE.
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***********************************************************************/
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/* Conversion between prediction filter coefficients and NLSFs */
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/* Requires the order to be an even number */
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/* A piecewise linear approximation maps LSF <-> cos(LSF) */
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/* Therefore the result is not accurate NLSFs, but the two */
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/* functions are accurate inverses of each other */
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#ifdef HAVE_CONFIG_H
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#include "config.h"
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#endif
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#include "SigProc_FIX.h"
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#include "tables.h"
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/* Number of binary divisions, when not in low complexity mode */
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#define BIN_DIV_STEPS_A2NLSF_FIX 3 /* must be no higher than 16 - log2( LSF_COS_TAB_SZ_FIX ) */
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#define MAX_ITERATIONS_A2NLSF_FIX 30
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/* Helper function for A2NLSF(..) */
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/* Transforms polynomials from cos(n*f) to cos(f)^n */
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static __inline void silk_A2NLSF_trans_poly(
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opus_int32 *p, /* I/O Polynomial */
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const opus_int dd /* I Polynomial order (= filter order / 2 ) */
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)
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{
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opus_int k, n;
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for( k = 2; k <= dd; k++ ) {
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for( n = dd; n > k; n-- ) {
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p[ n - 2 ] -= p[ n ];
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}
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p[ k - 2 ] -= silk_LSHIFT( p[ k ], 1 );
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}
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}
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/* Helper function for A2NLSF(..) */
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/* Polynomial evaluation */
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static __inline opus_int32 silk_A2NLSF_eval_poly( /* return the polynomial evaluation, in Q16 */
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opus_int32 *p, /* I Polynomial, Q16 */
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const opus_int32 x, /* I Evaluation point, Q12 */
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const opus_int dd /* I Order */
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)
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{
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opus_int n;
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opus_int32 x_Q16, y32;
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y32 = p[ dd ]; /* Q16 */
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x_Q16 = silk_LSHIFT( x, 4 );
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for( n = dd - 1; n >= 0; n-- ) {
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y32 = silk_SMLAWW( p[ n ], y32, x_Q16 ); /* Q16 */
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}
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return y32;
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}
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static __inline void silk_A2NLSF_init(
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const opus_int32 *a_Q16,
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opus_int32 *P,
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opus_int32 *Q,
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const opus_int dd
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)
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{
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opus_int k;
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/* Convert filter coefs to even and odd polynomials */
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P[dd] = silk_LSHIFT( 1, 16 );
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Q[dd] = silk_LSHIFT( 1, 16 );
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for( k = 0; k < dd; k++ ) {
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P[ k ] = -a_Q16[ dd - k - 1 ] - a_Q16[ dd + k ]; /* Q16 */
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Q[ k ] = -a_Q16[ dd - k - 1 ] + a_Q16[ dd + k ]; /* Q16 */
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}
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/* Divide out zeros as we have that for even filter orders, */
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/* z = 1 is always a root in Q, and */
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/* z = -1 is always a root in P */
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for( k = dd; k > 0; k-- ) {
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P[ k - 1 ] -= P[ k ];
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Q[ k - 1 ] += Q[ k ];
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}
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/* Transform polynomials from cos(n*f) to cos(f)^n */
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silk_A2NLSF_trans_poly( P, dd );
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silk_A2NLSF_trans_poly( Q, dd );
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}
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/* Compute Normalized Line Spectral Frequencies (NLSFs) from whitening filter coefficients */
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/* If not all roots are found, the a_Q16 coefficients are bandwidth expanded until convergence. */
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void silk_A2NLSF(
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opus_int16 *NLSF, /* O Normalized Line Spectral Frequencies in Q15 (0..2^15-1) [d] */
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opus_int32 *a_Q16, /* I/O Monic whitening filter coefficients in Q16 [d] */
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const opus_int d /* I Filter order (must be even) */
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)
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{
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opus_int i, k, m, dd, root_ix, ffrac;
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opus_int32 xlo, xhi, xmid;
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opus_int32 ylo, yhi, ymid, thr;
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opus_int32 nom, den;
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opus_int32 P[ SILK_MAX_ORDER_LPC / 2 + 1 ];
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opus_int32 Q[ SILK_MAX_ORDER_LPC / 2 + 1 ];
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opus_int32 *PQ[ 2 ];
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opus_int32 *p;
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/* Store pointers to array */
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PQ[ 0 ] = P;
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PQ[ 1 ] = Q;
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dd = silk_RSHIFT( d, 1 );
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silk_A2NLSF_init( a_Q16, P, Q, dd );
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/* Find roots, alternating between P and Q */
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p = P; /* Pointer to polynomial */
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xlo = silk_LSFCosTab_FIX_Q12[ 0 ]; /* Q12*/
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ylo = silk_A2NLSF_eval_poly( p, xlo, dd );
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if( ylo < 0 ) {
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/* Set the first NLSF to zero and move on to the next */
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NLSF[ 0 ] = 0;
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p = Q; /* Pointer to polynomial */
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ylo = silk_A2NLSF_eval_poly( p, xlo, dd );
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root_ix = 1; /* Index of current root */
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} else {
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root_ix = 0; /* Index of current root */
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}
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k = 1; /* Loop counter */
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i = 0; /* Counter for bandwidth expansions applied */
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thr = 0;
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while( 1 ) {
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/* Evaluate polynomial */
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xhi = silk_LSFCosTab_FIX_Q12[ k ]; /* Q12 */
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yhi = silk_A2NLSF_eval_poly( p, xhi, dd );
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/* Detect zero crossing */
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if( ( ylo <= 0 && yhi >= thr ) || ( ylo >= 0 && yhi <= -thr ) ) {
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if( yhi == 0 ) {
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/* If the root lies exactly at the end of the current */
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/* interval, look for the next root in the next interval */
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thr = 1;
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} else {
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thr = 0;
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}
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/* Binary division */
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ffrac = -256;
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for( m = 0; m < BIN_DIV_STEPS_A2NLSF_FIX; m++ ) {
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/* Evaluate polynomial */
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xmid = silk_RSHIFT_ROUND( xlo + xhi, 1 );
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ymid = silk_A2NLSF_eval_poly( p, xmid, dd );
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/* Detect zero crossing */
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if( ( ylo <= 0 && ymid >= 0 ) || ( ylo >= 0 && ymid <= 0 ) ) {
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/* Reduce frequency */
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xhi = xmid;
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yhi = ymid;
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} else {
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/* Increase frequency */
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xlo = xmid;
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ylo = ymid;
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ffrac = silk_ADD_RSHIFT( ffrac, 128, m );
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}
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}
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/* Interpolate */
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if( silk_abs( ylo ) < 65536 ) {
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/* Avoid dividing by zero */
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den = ylo - yhi;
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nom = silk_LSHIFT( ylo, 8 - BIN_DIV_STEPS_A2NLSF_FIX ) + silk_RSHIFT( den, 1 );
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if( den != 0 ) {
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ffrac += silk_DIV32( nom, den );
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}
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} else {
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/* No risk of dividing by zero because abs(ylo - yhi) >= abs(ylo) >= 65536 */
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ffrac += silk_DIV32( ylo, silk_RSHIFT( ylo - yhi, 8 - BIN_DIV_STEPS_A2NLSF_FIX ) );
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}
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NLSF[ root_ix ] = (opus_int16)silk_min_32( silk_LSHIFT( (opus_int32)k, 8 ) + ffrac, silk_int16_MAX );
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silk_assert( NLSF[ root_ix ] >= 0 );
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root_ix++; /* Next root */
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if( root_ix >= d ) {
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/* Found all roots */
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break;
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}
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/* Alternate pointer to polynomial */
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p = PQ[ root_ix & 1 ];
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/* Evaluate polynomial */
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xlo = silk_LSFCosTab_FIX_Q12[ k - 1 ]; /* Q12*/
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ylo = silk_LSHIFT( 1 - ( root_ix & 2 ), 12 );
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} else {
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/* Increment loop counter */
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k++;
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xlo = xhi;
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ylo = yhi;
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thr = 0;
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if( k > LSF_COS_TAB_SZ_FIX ) {
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i++;
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if( i > MAX_ITERATIONS_A2NLSF_FIX ) {
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/* Set NLSFs to white spectrum and exit */
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NLSF[ 0 ] = (opus_int16)silk_DIV32_16( 1 << 15, d + 1 );
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for( k = 1; k < d; k++ ) {
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NLSF[ k ] = (opus_int16)silk_SMULBB( k + 1, NLSF[ 0 ] );
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}
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return;
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}
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/* Error: Apply progressively more bandwidth expansion and run again */
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silk_bwexpander_32( a_Q16, d, 65536 - silk_SMULBB( 10 + i, i ) ); /* 10_Q16 = 0.00015*/
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silk_A2NLSF_init( a_Q16, P, Q, dd );
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p = P; /* Pointer to polynomial */
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xlo = silk_LSFCosTab_FIX_Q12[ 0 ]; /* Q12*/
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ylo = silk_A2NLSF_eval_poly( p, xlo, dd );
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if( ylo < 0 ) {
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/* Set the first NLSF to zero and move on to the next */
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NLSF[ 0 ] = 0;
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p = Q; /* Pointer to polynomial */
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ylo = silk_A2NLSF_eval_poly( p, xlo, dd );
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root_ix = 1; /* Index of current root */
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} else {
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root_ix = 0; /* Index of current root */
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}
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k = 1; /* Reset loop counter */
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}
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}
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}
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}
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