1 /*********************************************************************** 2 Copyright (c) 2006-2011, Skype Limited. All rights reserved. 3 Redistribution and use in source and binary forms, with or without 4 modification, are permitted provided that the following conditions 5 are met: 6 - Redistributions of source code must retain the above copyright notice, 7 this list of conditions and the following disclaimer. 8 - Redistributions in binary form must reproduce the above copyright 9 notice, this list of conditions and the following disclaimer in the 10 documentation and/or other materials provided with the distribution. 11 - Neither the name of Internet Society, IETF or IETF Trust, nor the 12 names of specific contributors, may be used to endorse or promote 13 products derived from this software without specific prior written 14 permission. 15 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS AS IS 16 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18 ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE 19 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 20 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 21 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 22 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 23 CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 24 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 25 POSSIBILITY OF SUCH DAMAGE. 26 ***********************************************************************/ 27 28 #ifdef HAVE_CONFIG_H 29 #include "config.h" 30 #endif 31 32 /* conversion between prediction filter coefficients and LSFs */ 33 /* order should be even */ 34 /* a piecewise linear approximation maps LSF <-> cos(LSF) */ 35 /* therefore the result is not accurate LSFs, but the two */ 36 /* functions are accurate inverses of each other */ 37 38 #include "SigProc_FIX.h" 39 #include "tables.h" 40 41 #define QA 16 42 43 /* helper function for NLSF2A(..) */ 44 static inline void silk_NLSF2A_find_poly( 45 opus_int32 *out, /* O intermediate polynomial, QA [dd+1] */ 46 const opus_int32 *cLSF, /* I vector of interleaved 2*cos(LSFs), QA [d] */ 47 opus_int dd /* I polynomial order (= 1/2 * filter order) */ 48 ) 49 { 50 opus_int k, n; 51 opus_int32 ftmp; 52 53 out[0] = silk_LSHIFT( 1, QA ); 54 out[1] = -cLSF[0]; 55 for( k = 1; k < dd; k++ ) { 56 ftmp = cLSF[2*k]; /* QA*/ 57 out[k+1] = silk_LSHIFT( out[k-1], 1 ) - (opus_int32)silk_RSHIFT_ROUND64( silk_SMULL( ftmp, out[k] ), QA ); 58 for( n = k; n > 1; n-- ) { 59 out[n] += out[n-2] - (opus_int32)silk_RSHIFT_ROUND64( silk_SMULL( ftmp, out[n-1] ), QA ); 60 } 61 out[1] -= ftmp; 62 } 63 } 64 65 /* compute whitening filter coefficients from normalized line spectral frequencies */ 66 void silk_NLSF2A( 67 opus_int16 *a_Q12, /* O monic whitening filter coefficients in Q12, [ d ] */ 68 const opus_int16 *NLSF, /* I normalized line spectral frequencies in Q15, [ d ] */ 69 const opus_int d /* I filter order (should be even) */ 70 ) 71 { 72 /* This ordering was found to maximize quality. It improves numerical accuracy of 73 silk_NLSF2A_find_poly() compared to "standard" ordering. */ 74 static const unsigned char ordering16[16] = { 75 0, 15, 8, 7, 4, 11, 12, 3, 2, 13, 10, 5, 6, 9, 14, 1 76 }; 77 static const unsigned char ordering10[10] = { 78 0, 9, 6, 3, 4, 5, 8, 1, 2, 7 79 }; 80 const unsigned char *ordering; 81 opus_int k, i, dd; 82 opus_int32 cos_LSF_QA[ SILK_MAX_ORDER_LPC ]; 83 opus_int32 P[ SILK_MAX_ORDER_LPC / 2 + 1 ], Q[ SILK_MAX_ORDER_LPC / 2 + 1 ]; 84 opus_int32 Ptmp, Qtmp, f_int, f_frac, cos_val, delta; 85 opus_int32 a32_QA1[ SILK_MAX_ORDER_LPC ]; 86 opus_int32 maxabs, absval, idx=0, sc_Q16; 87 88 silk_assert( LSF_COS_TAB_SZ_FIX == 128 ); 89 silk_assert( d==10||d==16 ); 90 91 /* convert LSFs to 2*cos(LSF), using piecewise linear curve from table */ 92 ordering = d == 16 ? ordering16 : ordering10; 93 for( k = 0; k < d; k++ ) { 94 silk_assert(NLSF[k] >= 0 ); 95 96 /* f_int on a scale 0-127 (rounded down) */ 97 f_int = silk_RSHIFT( NLSF[k], 15 - 7 ); 98 99 /* f_frac, range: 0..255 */ 100 f_frac = NLSF[k] - silk_LSHIFT( f_int, 15 - 7 ); 101 102 silk_assert(f_int >= 0); 103 silk_assert(f_int < LSF_COS_TAB_SZ_FIX ); 104 105 /* Read start and end value from table */ 106 cos_val = silk_LSFCosTab_FIX_Q12[ f_int ]; /* Q12 */ 107 delta = silk_LSFCosTab_FIX_Q12[ f_int + 1 ] - cos_val; /* Q12, with a range of 0..200 */ 108 109 /* Linear interpolation */ 110 cos_LSF_QA[ordering[k]] = silk_RSHIFT_ROUND( silk_LSHIFT( cos_val, 8 ) + silk_MUL( delta, f_frac ), 20 - QA ); /* QA */ 111 } 112 113 dd = silk_RSHIFT( d, 1 ); 114 115 /* generate even and odd polynomials using convolution */ 116 silk_NLSF2A_find_poly( P, &cos_LSF_QA[ 0 ], dd ); 117 silk_NLSF2A_find_poly( Q, &cos_LSF_QA[ 1 ], dd ); 118 119 /* convert even and odd polynomials to opus_int32 Q12 filter coefs */ 120 for( k = 0; k < dd; k++ ) { 121 Ptmp = P[ k+1 ] + P[ k ]; 122 Qtmp = Q[ k+1 ] - Q[ k ]; 123 124 /* the Ptmp and Qtmp values at this stage need to fit in int32 */ 125 a32_QA1[ k ] = -Qtmp - Ptmp; /* QA+1 */ 126 a32_QA1[ d-k-1 ] = Qtmp - Ptmp; /* QA+1 */ 127 } 128 129 /* Limit the maximum absolute value of the prediction coefficients, so that they'll fit in int16 */ 130 for( i = 0; i < 10; i++ ) { 131 /* Find maximum absolute value and its index */ 132 maxabs = 0; 133 for( k = 0; k < d; k++ ) { 134 absval = silk_abs( a32_QA1[k] ); 135 if( absval > maxabs ) { 136 maxabs = absval; 137 idx = k; 138 } 139 } 140 maxabs = silk_RSHIFT_ROUND( maxabs, QA + 1 - 12 ); /* QA+1 -> Q12 */ 141 142 if( maxabs > silk_int16_MAX ) { 143 /* Reduce magnitude of prediction coefficients */ 144 maxabs = silk_min( maxabs, 163838 ); /* ( silk_int32_MAX >> 14 ) + silk_int16_MAX = 163838 */ 145 sc_Q16 = SILK_FIX_CONST( 0.999, 16 ) - silk_DIV32( silk_LSHIFT( maxabs - silk_int16_MAX, 14 ), 146 silk_RSHIFT32( silk_MUL( maxabs, idx + 1), 2 ) ); 147 silk_bwexpander_32( a32_QA1, d, sc_Q16 ); 148 } else { 149 break; 150 } 151 } 152 153 if( i == 10 ) { 154 /* Reached the last iteration, clip the coefficients */ 155 for( k = 0; k < d; k++ ) { 156 a_Q12[ k ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( a32_QA1[ k ], QA + 1 - 12 ) ); /* QA+1 -> Q12 */ 157 a32_QA1[ k ] = silk_LSHIFT( (opus_int32)a_Q12[ k ], QA + 1 - 12 ); 158 } 159 } else { 160 for( k = 0; k < d; k++ ) { 161 a_Q12[ k ] = (opus_int16)silk_RSHIFT_ROUND( a32_QA1[ k ], QA + 1 - 12 ); /* QA+1 -> Q12 */ 162 } 163 } 164 165 for( i = 0; i < MAX_LPC_STABILIZE_ITERATIONS; i++ ) { 166 if( silk_LPC_inverse_pred_gain( a_Q12, d ) < SILK_FIX_CONST( 1.0 / MAX_PREDICTION_POWER_GAIN, 30 ) ) { 167 /* Prediction coefficients are (too close to) unstable; apply bandwidth expansion */ 168 /* on the unscaled coefficients, convert to Q12 and measure again */ 169 silk_bwexpander_32( a32_QA1, d, 65536 - silk_LSHIFT( 2, i ) ); 170 for( k = 0; k < d; k++ ) { 171 a_Q12[ k ] = (opus_int16)silk_RSHIFT_ROUND( a32_QA1[ k ], QA + 1 - 12 ); /* QA+1 -> Q12 */ 172 } 173 } else { 174 break; 175 } 176 } 177 } 178 179
