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+/***********************************************************************
+Copyright (c) 2006-2011, Skype Limited. All rights reserved.
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions
+are met:
+- Redistributions of source code must retain the above copyright notice,
+this list of conditions and the following disclaimer.
+- Redistributions in binary form must reproduce the above copyright
+notice, this list of conditions and the following disclaimer in the
+documentation and/or other materials provided with the distribution.
+- Neither the name of Internet Society, IETF or IETF Trust, nor the
+names of specific contributors, may be used to endorse or promote
+products derived from this software without specific prior written
+permission.
+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
+CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.
+***********************************************************************/
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+/* conversion between prediction filter coefficients and LSFs */
+/* order should be even */
+/* a piecewise linear approximation maps LSF <-> cos(LSF) */
+/* therefore the result is not accurate LSFs, but the two */
+/* functions are accurate inverses of each other */
+
+#include "SigProc_FIX.h"
+#include "tables.h"
+
+#define QA 16
+
+/* helper function for NLSF2A(..) */
+static OPUS_INLINE void silk_NLSF2A_find_poly(
+ opus_int32 *out, /* O intermediate polynomial, QA [dd+1] */
+ const opus_int32 *cLSF, /* I vector of interleaved 2*cos(LSFs), QA [d] */
+ opus_int dd /* I polynomial order (= 1/2 * filter order) */
+)
+{
+ opus_int k, n;
+ opus_int32 ftmp;
+
+ out[0] = silk_LSHIFT( 1, QA );
+ out[1] = -cLSF[0];
+ for( k = 1; k < dd; k++ ) {
+ ftmp = cLSF[2*k]; /* QA*/
+ out[k+1] = silk_LSHIFT( out[k-1], 1 ) - (opus_int32)silk_RSHIFT_ROUND64( silk_SMULL( ftmp, out[k] ), QA );
+ for( n = k; n > 1; n-- ) {
+ out[n] += out[n-2] - (opus_int32)silk_RSHIFT_ROUND64( silk_SMULL( ftmp, out[n-1] ), QA );
+ }
+ out[1] -= ftmp;
+ }
+}
+
+/* compute whitening filter coefficients from normalized line spectral frequencies */
+void silk_NLSF2A(
+ opus_int16 *a_Q12, /* O monic whitening filter coefficients in Q12, [ d ] */
+ const opus_int16 *NLSF, /* I normalized line spectral frequencies in Q15, [ d ] */
+ const opus_int d, /* I filter order (should be even) */
+ int arch /* I Run-time architecture */
+)
+{
+ /* This ordering was found to maximize quality. It improves numerical accuracy of
+ silk_NLSF2A_find_poly() compared to "standard" ordering. */
+ static const unsigned char ordering16[16] = {
+ 0, 15, 8, 7, 4, 11, 12, 3, 2, 13, 10, 5, 6, 9, 14, 1
+ };
+ static const unsigned char ordering10[10] = {
+ 0, 9, 6, 3, 4, 5, 8, 1, 2, 7
+ };
+ const unsigned char *ordering;
+ opus_int k, i, dd;
+ opus_int32 cos_LSF_QA[ SILK_MAX_ORDER_LPC ];
+ opus_int32 P[ SILK_MAX_ORDER_LPC / 2 + 1 ], Q[ SILK_MAX_ORDER_LPC / 2 + 1 ];
+ opus_int32 Ptmp, Qtmp, f_int, f_frac, cos_val, delta;
+ opus_int32 a32_QA1[ SILK_MAX_ORDER_LPC ];
+
+ silk_assert( LSF_COS_TAB_SZ_FIX == 128 );
+ celt_assert( d==10 || d==16 );
+
+ /* convert LSFs to 2*cos(LSF), using piecewise linear curve from table */
+ ordering = d == 16 ? ordering16 : ordering10;
+ for( k = 0; k < d; k++ ) {
+ silk_assert( NLSF[k] >= 0 );
+
+ /* f_int on a scale 0-127 (rounded down) */
+ f_int = silk_RSHIFT( NLSF[k], 15 - 7 );
+
+ /* f_frac, range: 0..255 */
+ f_frac = NLSF[k] - silk_LSHIFT( f_int, 15 - 7 );
+
+ silk_assert(f_int >= 0);
+ silk_assert(f_int < LSF_COS_TAB_SZ_FIX );
+
+ /* Read start and end value from table */
+ cos_val = silk_LSFCosTab_FIX_Q12[ f_int ]; /* Q12 */
+ delta = silk_LSFCosTab_FIX_Q12[ f_int + 1 ] - cos_val; /* Q12, with a range of 0..200 */
+
+ /* Linear interpolation */
+ cos_LSF_QA[ordering[k]] = silk_RSHIFT_ROUND( silk_LSHIFT( cos_val, 8 ) + silk_MUL( delta, f_frac ), 20 - QA ); /* QA */
+ }
+
+ dd = silk_RSHIFT( d, 1 );
+
+ /* generate even and odd polynomials using convolution */
+ silk_NLSF2A_find_poly( P, &cos_LSF_QA[ 0 ], dd );
+ silk_NLSF2A_find_poly( Q, &cos_LSF_QA[ 1 ], dd );
+
+ /* convert even and odd polynomials to opus_int32 Q12 filter coefs */
+ for( k = 0; k < dd; k++ ) {
+ Ptmp = P[ k+1 ] + P[ k ];
+ Qtmp = Q[ k+1 ] - Q[ k ];
+
+ /* the Ptmp and Qtmp values at this stage need to fit in int32 */
+ a32_QA1[ k ] = -Qtmp - Ptmp; /* QA+1 */
+ a32_QA1[ d-k-1 ] = Qtmp - Ptmp; /* QA+1 */
+ }
+
+ /* Convert int32 coefficients to Q12 int16 coefs */
+ silk_LPC_fit( a_Q12, a32_QA1, 12, QA + 1, d );
+
+ for( i = 0; silk_LPC_inverse_pred_gain( a_Q12, d, arch ) == 0 && i < MAX_LPC_STABILIZE_ITERATIONS; i++ ) {
+ /* Prediction coefficients are (too close to) unstable; apply bandwidth expansion */
+ /* on the unscaled coefficients, convert to Q12 and measure again */
+ silk_bwexpander_32( a32_QA1, d, 65536 - silk_LSHIFT( 2, i ) );
+ for( k = 0; k < d; k++ ) {
+ a_Q12[ k ] = (opus_int16)silk_RSHIFT_ROUND( a32_QA1[ k ], QA + 1 - 12 ); /* QA+1 -> Q12 */
+ }
+ }
+}
+