| /*********************************************************************** |
| Copyright (c) 2006-2011, Skype Limited. All rights reserved. |
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| 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 |
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| permission. |
| THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" |
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| ***********************************************************************/ |
| |
| /* Conversion between prediction filter coefficients and NLSFs */ |
| /* Requires the order to be an even number */ |
| /* A piecewise linear approximation maps LSF <-> cos(LSF) */ |
| /* Therefore the result is not accurate NLSFs, but the two */ |
| /* functions are accurate inverses of each other */ |
| |
| #ifdef HAVE_CONFIG_H |
| #include "config.h" |
| #endif |
| |
| #include "SigProc_FIX.h" |
| #include "tables.h" |
| |
| /* Number of binary divisions, when not in low complexity mode */ |
| #define BIN_DIV_STEPS_A2NLSF_FIX 3 /* must be no higher than 16 - log2( LSF_COS_TAB_SZ_FIX ) */ |
| #define MAX_ITERATIONS_A2NLSF_FIX 16 |
| |
| /* Helper function for A2NLSF(..) */ |
| /* Transforms polynomials from cos(n*f) to cos(f)^n */ |
| static OPUS_INLINE void silk_A2NLSF_trans_poly( |
| opus_int32 *p, /* I/O Polynomial */ |
| const opus_int dd /* I Polynomial order (= filter order / 2 ) */ |
| ) |
| { |
| opus_int k, n; |
| |
| for( k = 2; k <= dd; k++ ) { |
| for( n = dd; n > k; n-- ) { |
| p[ n - 2 ] -= p[ n ]; |
| } |
| p[ k - 2 ] -= silk_LSHIFT( p[ k ], 1 ); |
| } |
| } |
| /* Helper function for A2NLSF(..) */ |
| /* Polynomial evaluation */ |
| static OPUS_INLINE opus_int32 silk_A2NLSF_eval_poly( /* return the polynomial evaluation, in Q16 */ |
| opus_int32 *p, /* I Polynomial, Q16 */ |
| const opus_int32 x, /* I Evaluation point, Q12 */ |
| const opus_int dd /* I Order */ |
| ) |
| { |
| opus_int n; |
| opus_int32 x_Q16, y32; |
| |
| y32 = p[ dd ]; /* Q16 */ |
| x_Q16 = silk_LSHIFT( x, 4 ); |
| |
| if ( opus_likely( 8 == dd ) ) |
| { |
| y32 = silk_SMLAWW( p[ 7 ], y32, x_Q16 ); |
| y32 = silk_SMLAWW( p[ 6 ], y32, x_Q16 ); |
| y32 = silk_SMLAWW( p[ 5 ], y32, x_Q16 ); |
| y32 = silk_SMLAWW( p[ 4 ], y32, x_Q16 ); |
| y32 = silk_SMLAWW( p[ 3 ], y32, x_Q16 ); |
| y32 = silk_SMLAWW( p[ 2 ], y32, x_Q16 ); |
| y32 = silk_SMLAWW( p[ 1 ], y32, x_Q16 ); |
| y32 = silk_SMLAWW( p[ 0 ], y32, x_Q16 ); |
| } |
| else |
| { |
| for( n = dd - 1; n >= 0; n-- ) { |
| y32 = silk_SMLAWW( p[ n ], y32, x_Q16 ); /* Q16 */ |
| } |
| } |
| return y32; |
| } |
| |
| static OPUS_INLINE void silk_A2NLSF_init( |
| const opus_int32 *a_Q16, |
| opus_int32 *P, |
| opus_int32 *Q, |
| const opus_int dd |
| ) |
| { |
| opus_int k; |
| |
| /* Convert filter coefs to even and odd polynomials */ |
| P[dd] = silk_LSHIFT( 1, 16 ); |
| Q[dd] = silk_LSHIFT( 1, 16 ); |
| for( k = 0; k < dd; k++ ) { |
| P[ k ] = -a_Q16[ dd - k - 1 ] - a_Q16[ dd + k ]; /* Q16 */ |
| Q[ k ] = -a_Q16[ dd - k - 1 ] + a_Q16[ dd + k ]; /* Q16 */ |
| } |
| |
| /* Divide out zeros as we have that for even filter orders, */ |
| /* z = 1 is always a root in Q, and */ |
| /* z = -1 is always a root in P */ |
| for( k = dd; k > 0; k-- ) { |
| P[ k - 1 ] -= P[ k ]; |
| Q[ k - 1 ] += Q[ k ]; |
| } |
| |
| /* Transform polynomials from cos(n*f) to cos(f)^n */ |
| silk_A2NLSF_trans_poly( P, dd ); |
| silk_A2NLSF_trans_poly( Q, dd ); |
| } |
| |
| /* Compute Normalized Line Spectral Frequencies (NLSFs) from whitening filter coefficients */ |
| /* If not all roots are found, the a_Q16 coefficients are bandwidth expanded until convergence. */ |
| void silk_A2NLSF( |
| opus_int16 *NLSF, /* O Normalized Line Spectral Frequencies in Q15 (0..2^15-1) [d] */ |
| opus_int32 *a_Q16, /* I/O Monic whitening filter coefficients in Q16 [d] */ |
| const opus_int d /* I Filter order (must be even) */ |
| ) |
| { |
| opus_int i, k, m, dd, root_ix, ffrac; |
| opus_int32 xlo, xhi, xmid; |
| opus_int32 ylo, yhi, ymid, thr; |
| opus_int32 nom, den; |
| opus_int32 P[ SILK_MAX_ORDER_LPC / 2 + 1 ]; |
| opus_int32 Q[ SILK_MAX_ORDER_LPC / 2 + 1 ]; |
| opus_int32 *PQ[ 2 ]; |
| opus_int32 *p; |
| |
| /* Store pointers to array */ |
| PQ[ 0 ] = P; |
| PQ[ 1 ] = Q; |
| |
| dd = silk_RSHIFT( d, 1 ); |
| |
| silk_A2NLSF_init( a_Q16, P, Q, dd ); |
| |
| /* Find roots, alternating between P and Q */ |
| p = P; /* Pointer to polynomial */ |
| |
| xlo = silk_LSFCosTab_FIX_Q12[ 0 ]; /* Q12*/ |
| ylo = silk_A2NLSF_eval_poly( p, xlo, dd ); |
| |
| if( ylo < 0 ) { |
| /* Set the first NLSF to zero and move on to the next */ |
| NLSF[ 0 ] = 0; |
| p = Q; /* Pointer to polynomial */ |
| ylo = silk_A2NLSF_eval_poly( p, xlo, dd ); |
| root_ix = 1; /* Index of current root */ |
| } else { |
| root_ix = 0; /* Index of current root */ |
| } |
| k = 1; /* Loop counter */ |
| i = 0; /* Counter for bandwidth expansions applied */ |
| thr = 0; |
| while( 1 ) { |
| /* Evaluate polynomial */ |
| xhi = silk_LSFCosTab_FIX_Q12[ k ]; /* Q12 */ |
| yhi = silk_A2NLSF_eval_poly( p, xhi, dd ); |
| |
| /* Detect zero crossing */ |
| if( ( ylo <= 0 && yhi >= thr ) || ( ylo >= 0 && yhi <= -thr ) ) { |
| if( yhi == 0 ) { |
| /* If the root lies exactly at the end of the current */ |
| /* interval, look for the next root in the next interval */ |
| thr = 1; |
| } else { |
| thr = 0; |
| } |
| /* Binary division */ |
| ffrac = -256; |
| for( m = 0; m < BIN_DIV_STEPS_A2NLSF_FIX; m++ ) { |
| /* Evaluate polynomial */ |
| xmid = silk_RSHIFT_ROUND( xlo + xhi, 1 ); |
| ymid = silk_A2NLSF_eval_poly( p, xmid, dd ); |
| |
| /* Detect zero crossing */ |
| if( ( ylo <= 0 && ymid >= 0 ) || ( ylo >= 0 && ymid <= 0 ) ) { |
| /* Reduce frequency */ |
| xhi = xmid; |
| yhi = ymid; |
| } else { |
| /* Increase frequency */ |
| xlo = xmid; |
| ylo = ymid; |
| ffrac = silk_ADD_RSHIFT( ffrac, 128, m ); |
| } |
| } |
| |
| /* Interpolate */ |
| if( silk_abs( ylo ) < 65536 ) { |
| /* Avoid dividing by zero */ |
| den = ylo - yhi; |
| nom = silk_LSHIFT( ylo, 8 - BIN_DIV_STEPS_A2NLSF_FIX ) + silk_RSHIFT( den, 1 ); |
| if( den != 0 ) { |
| ffrac += silk_DIV32( nom, den ); |
| } |
| } else { |
| /* No risk of dividing by zero because abs(ylo - yhi) >= abs(ylo) >= 65536 */ |
| ffrac += silk_DIV32( ylo, silk_RSHIFT( ylo - yhi, 8 - BIN_DIV_STEPS_A2NLSF_FIX ) ); |
| } |
| NLSF[ root_ix ] = (opus_int16)silk_min_32( silk_LSHIFT( (opus_int32)k, 8 ) + ffrac, silk_int16_MAX ); |
| |
| silk_assert( NLSF[ root_ix ] >= 0 ); |
| |
| root_ix++; /* Next root */ |
| if( root_ix >= d ) { |
| /* Found all roots */ |
| break; |
| } |
| /* Alternate pointer to polynomial */ |
| p = PQ[ root_ix & 1 ]; |
| |
| /* Evaluate polynomial */ |
| xlo = silk_LSFCosTab_FIX_Q12[ k - 1 ]; /* Q12*/ |
| ylo = silk_LSHIFT( 1 - ( root_ix & 2 ), 12 ); |
| } else { |
| /* Increment loop counter */ |
| k++; |
| xlo = xhi; |
| ylo = yhi; |
| thr = 0; |
| |
| if( k > LSF_COS_TAB_SZ_FIX ) { |
| i++; |
| if( i > MAX_ITERATIONS_A2NLSF_FIX ) { |
| /* Set NLSFs to white spectrum and exit */ |
| NLSF[ 0 ] = (opus_int16)silk_DIV32_16( 1 << 15, d + 1 ); |
| for( k = 1; k < d; k++ ) { |
| NLSF[ k ] = (opus_int16)silk_ADD16( NLSF[ k-1 ], NLSF[ 0 ] ); |
| } |
| return; |
| } |
| |
| /* Error: Apply progressively more bandwidth expansion and run again */ |
| silk_bwexpander_32( a_Q16, d, 65536 - silk_LSHIFT( 1, i ) ); |
| |
| silk_A2NLSF_init( a_Q16, P, Q, dd ); |
| p = P; /* Pointer to polynomial */ |
| xlo = silk_LSFCosTab_FIX_Q12[ 0 ]; /* Q12*/ |
| ylo = silk_A2NLSF_eval_poly( p, xlo, dd ); |
| if( ylo < 0 ) { |
| /* Set the first NLSF to zero and move on to the next */ |
| NLSF[ 0 ] = 0; |
| p = Q; /* Pointer to polynomial */ |
| ylo = silk_A2NLSF_eval_poly( p, xlo, dd ); |
| root_ix = 1; /* Index of current root */ |
| } else { |
| root_ix = 0; /* Index of current root */ |
| } |
| k = 1; /* Reset loop counter */ |
| } |
| } |
| } |
| } |
