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| products derived from this software without specific prior written |
| permission. |
| THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" |
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| ***********************************************************************/ |
| |
| #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 */ |
| } |
| } |
| } |
| |
