michael@0: /***********************************************************************
michael@0: Copyright (c) 2006-2011, Skype Limited. All rights reserved.
michael@0: Redistribution and use in source and binary forms, with or without
michael@0: modification, are permitted provided that the following conditions
michael@0: are met:
michael@0: - Redistributions of source code must retain the above copyright notice,
michael@0: this list of conditions and the following disclaimer.
michael@0: - Redistributions in binary form must reproduce the above copyright
michael@0: notice, this list of conditions and the following disclaimer in the
michael@0: documentation and/or other materials provided with the distribution.
michael@0: - Neither the name of Internet Society, IETF or IETF Trust, nor the
michael@0: names of specific contributors, may be used to endorse or promote
michael@0: products derived from this software without specific prior written
michael@0: permission.
michael@0: THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
michael@0: AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
michael@0: IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
michael@0: ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
michael@0: LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
michael@0: CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
michael@0: SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
michael@0: INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
michael@0: CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
michael@0: ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
michael@0: POSSIBILITY OF SUCH DAMAGE.
michael@0: ***********************************************************************/
michael@0: 
michael@0: #ifdef HAVE_CONFIG_H
michael@0: #include "config.h"
michael@0: #endif
michael@0: 
michael@0: /* conversion between prediction filter coefficients and LSFs   */
michael@0: /* order should be even                                         */
michael@0: /* a piecewise linear approximation maps LSF <-> cos(LSF)       */
michael@0: /* therefore the result is not accurate LSFs, but the two       */
michael@0: /* functions are accurate inverses of each other                */
michael@0: 
michael@0: #include "SigProc_FIX.h"
michael@0: #include "tables.h"
michael@0: 
michael@0: #define QA      16
michael@0: 
michael@0: /* helper function for NLSF2A(..) */
michael@0: static OPUS_INLINE void silk_NLSF2A_find_poly(
michael@0:     opus_int32          *out,      /* O    intermediate polynomial, QA [dd+1]        */
michael@0:     const opus_int32    *cLSF,     /* I    vector of interleaved 2*cos(LSFs), QA [d] */
michael@0:     opus_int            dd         /* I    polynomial order (= 1/2 * filter order)   */
michael@0: )
michael@0: {
michael@0:     opus_int   k, n;
michael@0:     opus_int32 ftmp;
michael@0: 
michael@0:     out[0] = silk_LSHIFT( 1, QA );
michael@0:     out[1] = -cLSF[0];
michael@0:     for( k = 1; k < dd; k++ ) {
michael@0:         ftmp = cLSF[2*k];            /* QA*/
michael@0:         out[k+1] = silk_LSHIFT( out[k-1], 1 ) - (opus_int32)silk_RSHIFT_ROUND64( silk_SMULL( ftmp, out[k] ), QA );
michael@0:         for( n = k; n > 1; n-- ) {
michael@0:             out[n] += out[n-2] - (opus_int32)silk_RSHIFT_ROUND64( silk_SMULL( ftmp, out[n-1] ), QA );
michael@0:         }
michael@0:         out[1] -= ftmp;
michael@0:     }
michael@0: }
michael@0: 
michael@0: /* compute whitening filter coefficients from normalized line spectral frequencies */
michael@0: void silk_NLSF2A(
michael@0:     opus_int16                  *a_Q12,             /* O    monic whitening filter coefficients in Q12,  [ d ]          */
michael@0:     const opus_int16            *NLSF,              /* I    normalized line spectral frequencies in Q15, [ d ]          */
michael@0:     const opus_int              d                   /* I    filter order (should be even)                               */
michael@0: )
michael@0: {
michael@0:     /* This ordering was found to maximize quality. It improves numerical accuracy of
michael@0:        silk_NLSF2A_find_poly() compared to "standard" ordering. */
michael@0:     static const unsigned char ordering16[16] = {
michael@0:       0, 15, 8, 7, 4, 11, 12, 3, 2, 13, 10, 5, 6, 9, 14, 1
michael@0:     };
michael@0:     static const unsigned char ordering10[10] = {
michael@0:       0, 9, 6, 3, 4, 5, 8, 1, 2, 7
michael@0:     };
michael@0:     const unsigned char *ordering;
michael@0:     opus_int   k, i, dd;
michael@0:     opus_int32 cos_LSF_QA[ SILK_MAX_ORDER_LPC ];
michael@0:     opus_int32 P[ SILK_MAX_ORDER_LPC / 2 + 1 ], Q[ SILK_MAX_ORDER_LPC / 2 + 1 ];
michael@0:     opus_int32 Ptmp, Qtmp, f_int, f_frac, cos_val, delta;
michael@0:     opus_int32 a32_QA1[ SILK_MAX_ORDER_LPC ];
michael@0:     opus_int32 maxabs, absval, idx=0, sc_Q16;
michael@0: 
michael@0:     silk_assert( LSF_COS_TAB_SZ_FIX == 128 );
michael@0:     silk_assert( d==10||d==16 );
michael@0: 
michael@0:     /* convert LSFs to 2*cos(LSF), using piecewise linear curve from table */
michael@0:     ordering = d == 16 ? ordering16 : ordering10;
michael@0:     for( k = 0; k < d; k++ ) {
michael@0:         silk_assert(NLSF[k] >= 0 );
michael@0: 
michael@0:         /* f_int on a scale 0-127 (rounded down) */
michael@0:         f_int = silk_RSHIFT( NLSF[k], 15 - 7 );
michael@0: 
michael@0:         /* f_frac, range: 0..255 */
michael@0:         f_frac = NLSF[k] - silk_LSHIFT( f_int, 15 - 7 );
michael@0: 
michael@0:         silk_assert(f_int >= 0);
michael@0:         silk_assert(f_int < LSF_COS_TAB_SZ_FIX );
michael@0: 
michael@0:         /* Read start and end value from table */
michael@0:         cos_val = silk_LSFCosTab_FIX_Q12[ f_int ];                /* Q12 */
michael@0:         delta   = silk_LSFCosTab_FIX_Q12[ f_int + 1 ] - cos_val;  /* Q12, with a range of 0..200 */
michael@0: 
michael@0:         /* Linear interpolation */
michael@0:         cos_LSF_QA[ordering[k]] = silk_RSHIFT_ROUND( silk_LSHIFT( cos_val, 8 ) + silk_MUL( delta, f_frac ), 20 - QA ); /* QA */
michael@0:     }
michael@0: 
michael@0:     dd = silk_RSHIFT( d, 1 );
michael@0: 
michael@0:     /* generate even and odd polynomials using convolution */
michael@0:     silk_NLSF2A_find_poly( P, &cos_LSF_QA[ 0 ], dd );
michael@0:     silk_NLSF2A_find_poly( Q, &cos_LSF_QA[ 1 ], dd );
michael@0: 
michael@0:     /* convert even and odd polynomials to opus_int32 Q12 filter coefs */
michael@0:     for( k = 0; k < dd; k++ ) {
michael@0:         Ptmp = P[ k+1 ] + P[ k ];
michael@0:         Qtmp = Q[ k+1 ] - Q[ k ];
michael@0: 
michael@0:         /* the Ptmp and Qtmp values at this stage need to fit in int32 */
michael@0:         a32_QA1[ k ]     = -Qtmp - Ptmp;        /* QA+1 */
michael@0:         a32_QA1[ d-k-1 ] =  Qtmp - Ptmp;        /* QA+1 */
michael@0:     }
michael@0: 
michael@0:     /* Limit the maximum absolute value of the prediction coefficients, so that they'll fit in int16 */
michael@0:     for( i = 0; i < 10; i++ ) {
michael@0:         /* Find maximum absolute value and its index */
michael@0:         maxabs = 0;
michael@0:         for( k = 0; k < d; k++ ) {
michael@0:             absval = silk_abs( a32_QA1[k] );
michael@0:             if( absval > maxabs ) {
michael@0:                 maxabs = absval;
michael@0:                 idx    = k;
michael@0:             }
michael@0:         }
michael@0:         maxabs = silk_RSHIFT_ROUND( maxabs, QA + 1 - 12 );                                          /* QA+1 -> Q12 */
michael@0: 
michael@0:         if( maxabs > silk_int16_MAX ) {
michael@0:             /* Reduce magnitude of prediction coefficients */
michael@0:             maxabs = silk_min( maxabs, 163838 );  /* ( silk_int32_MAX >> 14 ) + silk_int16_MAX = 163838 */
michael@0:             sc_Q16 = SILK_FIX_CONST( 0.999, 16 ) - silk_DIV32( silk_LSHIFT( maxabs - silk_int16_MAX, 14 ),
michael@0:                                         silk_RSHIFT32( silk_MUL( maxabs, idx + 1), 2 ) );
michael@0:             silk_bwexpander_32( a32_QA1, d, sc_Q16 );
michael@0:         } else {
michael@0:             break;
michael@0:         }
michael@0:     }
michael@0: 
michael@0:     if( i == 10 ) {
michael@0:         /* Reached the last iteration, clip the coefficients */
michael@0:         for( k = 0; k < d; k++ ) {
michael@0:             a_Q12[ k ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( a32_QA1[ k ], QA + 1 - 12 ) );  /* QA+1 -> Q12 */
michael@0:             a32_QA1[ k ] = silk_LSHIFT( (opus_int32)a_Q12[ k ], QA + 1 - 12 );
michael@0:         }
michael@0:     } else {
michael@0:         for( k = 0; k < d; k++ ) {
michael@0:             a_Q12[ k ] = (opus_int16)silk_RSHIFT_ROUND( a32_QA1[ k ], QA + 1 - 12 );                /* QA+1 -> Q12 */
michael@0:         }
michael@0:     }
michael@0: 
michael@0:     for( i = 0; i < MAX_LPC_STABILIZE_ITERATIONS; i++ ) {
michael@0:         if( silk_LPC_inverse_pred_gain( a_Q12, d ) < SILK_FIX_CONST( 1.0 / MAX_PREDICTION_POWER_GAIN, 30 ) ) {
michael@0:             /* Prediction coefficients are (too close to) unstable; apply bandwidth expansion   */
michael@0:             /* on the unscaled coefficients, convert to Q12 and measure again                   */
michael@0:             silk_bwexpander_32( a32_QA1, d, 65536 - silk_LSHIFT( 2, i ) );
michael@0:             for( k = 0; k < d; k++ ) {
michael@0:                 a_Q12[ k ] = (opus_int16)silk_RSHIFT_ROUND( a32_QA1[ k ], QA + 1 - 12 );            /* QA+1 -> Q12 */
michael@0:             }
michael@0:         } else {
michael@0:             break;
michael@0:         }
michael@0:     }
michael@0: }
michael@0: