Chris@69: /***********************************************************************
Chris@69: Copyright (c) 2006-2011, Skype Limited. All rights reserved.
Chris@69: Redistribution and use in source and binary forms, with or without
Chris@69: modification, are permitted provided that the following conditions
Chris@69: are met:
Chris@69: - Redistributions of source code must retain the above copyright notice,
Chris@69: this list of conditions and the following disclaimer.
Chris@69: - Redistributions in binary form must reproduce the above copyright
Chris@69: notice, this list of conditions and the following disclaimer in the
Chris@69: documentation and/or other materials provided with the distribution.
Chris@69: - Neither the name of Internet Society, IETF or IETF Trust, nor the
Chris@69: names of specific contributors, may be used to endorse or promote
Chris@69: products derived from this software without specific prior written
Chris@69: permission.
Chris@69: THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
Chris@69: AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
Chris@69: IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
Chris@69: ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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Chris@69: INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
Chris@69: CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
Chris@69: ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
Chris@69: POSSIBILITY OF SUCH DAMAGE.
Chris@69: ***********************************************************************/
Chris@69: 
Chris@69: #ifdef HAVE_CONFIG_H
Chris@69: #include "config.h"
Chris@69: #endif
Chris@69: 
Chris@69: /* conversion between prediction filter coefficients and LSFs   */
Chris@69: /* order should be even                                         */
Chris@69: /* a piecewise linear approximation maps LSF <-> cos(LSF)       */
Chris@69: /* therefore the result is not accurate LSFs, but the two       */
Chris@69: /* functions are accurate inverses of each other                */
Chris@69: 
Chris@69: #include "SigProc_FIX.h"
Chris@69: #include "tables.h"
Chris@69: 
Chris@69: #define QA      16
Chris@69: 
Chris@69: /* helper function for NLSF2A(..) */
Chris@69: static OPUS_INLINE void silk_NLSF2A_find_poly(
Chris@69:     opus_int32          *out,      /* O    intermediate polynomial, QA [dd+1]        */
Chris@69:     const opus_int32    *cLSF,     /* I    vector of interleaved 2*cos(LSFs), QA [d] */
Chris@69:     opus_int            dd         /* I    polynomial order (= 1/2 * filter order)   */
Chris@69: )
Chris@69: {
Chris@69:     opus_int   k, n;
Chris@69:     opus_int32 ftmp;
Chris@69: 
Chris@69:     out[0] = silk_LSHIFT( 1, QA );
Chris@69:     out[1] = -cLSF[0];
Chris@69:     for( k = 1; k < dd; k++ ) {
Chris@69:         ftmp = cLSF[2*k];            /* QA*/
Chris@69:         out[k+1] = silk_LSHIFT( out[k-1], 1 ) - (opus_int32)silk_RSHIFT_ROUND64( silk_SMULL( ftmp, out[k] ), QA );
Chris@69:         for( n = k; n > 1; n-- ) {
Chris@69:             out[n] += out[n-2] - (opus_int32)silk_RSHIFT_ROUND64( silk_SMULL( ftmp, out[n-1] ), QA );
Chris@69:         }
Chris@69:         out[1] -= ftmp;
Chris@69:     }
Chris@69: }
Chris@69: 
Chris@69: /* compute whitening filter coefficients from normalized line spectral frequencies */
Chris@69: void silk_NLSF2A(
Chris@69:     opus_int16                  *a_Q12,             /* O    monic whitening filter coefficients in Q12,  [ d ]          */
Chris@69:     const opus_int16            *NLSF,              /* I    normalized line spectral frequencies in Q15, [ d ]          */
Chris@69:     const opus_int              d,                  /* I    filter order (should be even)                               */
Chris@69:     int                         arch                /* I    Run-time architecture                                       */
Chris@69: )
Chris@69: {
Chris@69:     /* This ordering was found to maximize quality. It improves numerical accuracy of
Chris@69:        silk_NLSF2A_find_poly() compared to "standard" ordering. */
Chris@69:     static const unsigned char ordering16[16] = {
Chris@69:       0, 15, 8, 7, 4, 11, 12, 3, 2, 13, 10, 5, 6, 9, 14, 1
Chris@69:     };
Chris@69:     static const unsigned char ordering10[10] = {
Chris@69:       0, 9, 6, 3, 4, 5, 8, 1, 2, 7
Chris@69:     };
Chris@69:     const unsigned char *ordering;
Chris@69:     opus_int   k, i, dd;
Chris@69:     opus_int32 cos_LSF_QA[ SILK_MAX_ORDER_LPC ];
Chris@69:     opus_int32 P[ SILK_MAX_ORDER_LPC / 2 + 1 ], Q[ SILK_MAX_ORDER_LPC / 2 + 1 ];
Chris@69:     opus_int32 Ptmp, Qtmp, f_int, f_frac, cos_val, delta;
Chris@69:     opus_int32 a32_QA1[ SILK_MAX_ORDER_LPC ];
Chris@69: 
Chris@69:     silk_assert( LSF_COS_TAB_SZ_FIX == 128 );
Chris@69:     celt_assert( d==10 || d==16 );
Chris@69: 
Chris@69:     /* convert LSFs to 2*cos(LSF), using piecewise linear curve from table */
Chris@69:     ordering = d == 16 ? ordering16 : ordering10;
Chris@69:     for( k = 0; k < d; k++ ) {
Chris@69:         silk_assert( NLSF[k] >= 0 );
Chris@69: 
Chris@69:         /* f_int on a scale 0-127 (rounded down) */
Chris@69:         f_int = silk_RSHIFT( NLSF[k], 15 - 7 );
Chris@69: 
Chris@69:         /* f_frac, range: 0..255 */
Chris@69:         f_frac = NLSF[k] - silk_LSHIFT( f_int, 15 - 7 );
Chris@69: 
Chris@69:         silk_assert(f_int >= 0);
Chris@69:         silk_assert(f_int < LSF_COS_TAB_SZ_FIX );
Chris@69: 
Chris@69:         /* Read start and end value from table */
Chris@69:         cos_val = silk_LSFCosTab_FIX_Q12[ f_int ];                /* Q12 */
Chris@69:         delta   = silk_LSFCosTab_FIX_Q12[ f_int + 1 ] - cos_val;  /* Q12, with a range of 0..200 */
Chris@69: 
Chris@69:         /* Linear interpolation */
Chris@69:         cos_LSF_QA[ordering[k]] = silk_RSHIFT_ROUND( silk_LSHIFT( cos_val, 8 ) + silk_MUL( delta, f_frac ), 20 - QA ); /* QA */
Chris@69:     }
Chris@69: 
Chris@69:     dd = silk_RSHIFT( d, 1 );
Chris@69: 
Chris@69:     /* generate even and odd polynomials using convolution */
Chris@69:     silk_NLSF2A_find_poly( P, &cos_LSF_QA[ 0 ], dd );
Chris@69:     silk_NLSF2A_find_poly( Q, &cos_LSF_QA[ 1 ], dd );
Chris@69: 
Chris@69:     /* convert even and odd polynomials to opus_int32 Q12 filter coefs */
Chris@69:     for( k = 0; k < dd; k++ ) {
Chris@69:         Ptmp = P[ k+1 ] + P[ k ];
Chris@69:         Qtmp = Q[ k+1 ] - Q[ k ];
Chris@69: 
Chris@69:         /* the Ptmp and Qtmp values at this stage need to fit in int32 */
Chris@69:         a32_QA1[ k ]     = -Qtmp - Ptmp;        /* QA+1 */
Chris@69:         a32_QA1[ d-k-1 ] =  Qtmp - Ptmp;        /* QA+1 */
Chris@69:     }
Chris@69: 
Chris@69:     /* Convert int32 coefficients to Q12 int16 coefs */
Chris@69:     silk_LPC_fit( a_Q12, a32_QA1, 12, QA + 1, d );
Chris@69: 
Chris@69:     for( i = 0; silk_LPC_inverse_pred_gain( a_Q12, d, arch ) == 0 && i < MAX_LPC_STABILIZE_ITERATIONS; i++ ) {
Chris@69:         /* Prediction coefficients are (too close to) unstable; apply bandwidth expansion   */
Chris@69:         /* on the unscaled coefficients, convert to Q12 and measure again                   */
Chris@69:         silk_bwexpander_32( a32_QA1, d, 65536 - silk_LSHIFT( 2, i ) );
Chris@69:         for( k = 0; k < d; k++ ) {
Chris@69:             a_Q12[ k ] = (opus_int16)silk_RSHIFT_ROUND( a32_QA1[ k ], QA + 1 - 12 );            /* QA+1 -> Q12 */
Chris@69:         }
Chris@69:     }
Chris@69: }
Chris@69: