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 /* Conversion between prediction filter coefficients and NLSFs */ 29 /* Requires the order to be an even number */ 30 /* A piecewise linear approximation maps LSF <-> cos(LSF) */ 31 /* Therefore the result is not accurate NLSFs, but the two */ 32 /* functions are accurate inverses of each other */ 33 34 #ifdef HAVE_CONFIG_H 35 #include "config.h" 36 #endif 37 38 #include "SigProc_FIX.h" 39 #include "tables.h" 40 41 /* Number of binary divisions, when not in low complexity mode */ 42 #define BIN_DIV_STEPS_A2NLSF_FIX 3 /* must be no higher than 16 - log2( LSF_COS_TAB_SZ_FIX ) */ 43 #define MAX_ITERATIONS_A2NLSF_FIX 30 44 45 /* Helper function for A2NLSF(..) */ 46 /* Transforms polynomials from cos(n*f) to cos(f)^n */ 47 static inline void silk_A2NLSF_trans_poly( 48 opus_int32 *p, /* I/O Polynomial */ 49 const opus_int dd /* I Polynomial order (= filter order / 2 ) */ 50 ) 51 { 52 opus_int k, n; 53 54 for( k = 2; k <= dd; k++ ) { 55 for( n = dd; n > k; n-- ) { 56 p[ n - 2 ] -= p[ n ]; 57 } 58 p[ k - 2 ] -= silk_LSHIFT( p[ k ], 1 ); 59 } 60 } 61 /* Helper function for A2NLSF(..) */ 62 /* Polynomial evaluation */ 63 static inline opus_int32 silk_A2NLSF_eval_poly( /* return the polynomial evaluation, in Q16 */ 64 opus_int32 *p, /* I Polynomial, Q16 */ 65 const opus_int32 x, /* I Evaluation point, Q12 */ 66 const opus_int dd /* I Order */ 67 ) 68 { 69 opus_int n; 70 opus_int32 x_Q16, y32; 71 72 y32 = p[ dd ]; /* Q16 */ 73 x_Q16 = silk_LSHIFT( x, 4 ); 74 for( n = dd - 1; n >= 0; n-- ) { 75 y32 = silk_SMLAWW( p[ n ], y32, x_Q16 ); /* Q16 */ 76 } 77 return y32; 78 } 79 80 static inline void silk_A2NLSF_init( 81 const opus_int32 *a_Q16, 82 opus_int32 *P, 83 opus_int32 *Q, 84 const opus_int dd 85 ) 86 { 87 opus_int k; 88 89 /* Convert filter coefs to even and odd polynomials */ 90 P[dd] = silk_LSHIFT( 1, 16 ); 91 Q[dd] = silk_LSHIFT( 1, 16 ); 92 for( k = 0; k < dd; k++ ) { 93 P[ k ] = -a_Q16[ dd - k - 1 ] - a_Q16[ dd + k ]; /* Q16 */ 94 Q[ k ] = -a_Q16[ dd - k - 1 ] + a_Q16[ dd + k ]; /* Q16 */ 95 } 96 97 /* Divide out zeros as we have that for even filter orders, */ 98 /* z = 1 is always a root in Q, and */ 99 /* z = -1 is always a root in P */ 100 for( k = dd; k > 0; k-- ) { 101 P[ k - 1 ] -= P[ k ]; 102 Q[ k - 1 ] += Q[ k ]; 103 } 104 105 /* Transform polynomials from cos(n*f) to cos(f)^n */ 106 silk_A2NLSF_trans_poly( P, dd ); 107 silk_A2NLSF_trans_poly( Q, dd ); 108 } 109 110 /* Compute Normalized Line Spectral Frequencies (NLSFs) from whitening filter coefficients */ 111 /* If not all roots are found, the a_Q16 coefficients are bandwidth expanded until convergence. */ 112 void silk_A2NLSF( 113 opus_int16 *NLSF, /* O Normalized Line Spectral Frequencies in Q15 (0..2^15-1) [d] */ 114 opus_int32 *a_Q16, /* I/O Monic whitening filter coefficients in Q16 [d] */ 115 const opus_int d /* I Filter order (must be even) */ 116 ) 117 { 118 opus_int i, k, m, dd, root_ix, ffrac; 119 opus_int32 xlo, xhi, xmid; 120 opus_int32 ylo, yhi, ymid, thr; 121 opus_int32 nom, den; 122 opus_int32 P[ SILK_MAX_ORDER_LPC / 2 + 1 ]; 123 opus_int32 Q[ SILK_MAX_ORDER_LPC / 2 + 1 ]; 124 opus_int32 *PQ[ 2 ]; 125 opus_int32 *p; 126 127 /* Store pointers to array */ 128 PQ[ 0 ] = P; 129 PQ[ 1 ] = Q; 130 131 dd = silk_RSHIFT( d, 1 ); 132 133 silk_A2NLSF_init( a_Q16, P, Q, dd ); 134 135 /* Find roots, alternating between P and Q */ 136 p = P; /* Pointer to polynomial */ 137 138 xlo = silk_LSFCosTab_FIX_Q12[ 0 ]; /* Q12*/ 139 ylo = silk_A2NLSF_eval_poly( p, xlo, dd ); 140 141 if( ylo < 0 ) { 142 /* Set the first NLSF to zero and move on to the next */ 143 NLSF[ 0 ] = 0; 144 p = Q; /* Pointer to polynomial */ 145 ylo = silk_A2NLSF_eval_poly( p, xlo, dd ); 146 root_ix = 1; /* Index of current root */ 147 } else { 148 root_ix = 0; /* Index of current root */ 149 } 150 k = 1; /* Loop counter */ 151 i = 0; /* Counter for bandwidth expansions applied */ 152 thr = 0; 153 while( 1 ) { 154 /* Evaluate polynomial */ 155 xhi = silk_LSFCosTab_FIX_Q12[ k ]; /* Q12 */ 156 yhi = silk_A2NLSF_eval_poly( p, xhi, dd ); 157 158 /* Detect zero crossing */ 159 if( ( ylo <= 0 && yhi >= thr ) || ( ylo >= 0 && yhi <= -thr ) ) { 160 if( yhi == 0 ) { 161 /* If the root lies exactly at the end of the current */ 162 /* interval, look for the next root in the next interval */ 163 thr = 1; 164 } else { 165 thr = 0; 166 } 167 /* Binary division */ 168 ffrac = -256; 169 for( m = 0; m < BIN_DIV_STEPS_A2NLSF_FIX; m++ ) { 170 /* Evaluate polynomial */ 171 xmid = silk_RSHIFT_ROUND( xlo + xhi, 1 ); 172 ymid = silk_A2NLSF_eval_poly( p, xmid, dd ); 173 174 /* Detect zero crossing */ 175 if( ( ylo <= 0 && ymid >= 0 ) || ( ylo >= 0 && ymid <= 0 ) ) { 176 /* Reduce frequency */ 177 xhi = xmid; 178 yhi = ymid; 179 } else { 180 /* Increase frequency */ 181 xlo = xmid; 182 ylo = ymid; 183 ffrac = silk_ADD_RSHIFT( ffrac, 128, m ); 184 } 185 } 186 187 /* Interpolate */ 188 if( silk_abs( ylo ) < 65536 ) { 189 /* Avoid dividing by zero */ 190 den = ylo - yhi; 191 nom = silk_LSHIFT( ylo, 8 - BIN_DIV_STEPS_A2NLSF_FIX ) + silk_RSHIFT( den, 1 ); 192 if( den != 0 ) { 193 ffrac += silk_DIV32( nom, den ); 194 } 195 } else { 196 /* No risk of dividing by zero because abs(ylo - yhi) >= abs(ylo) >= 65536 */ 197 ffrac += silk_DIV32( ylo, silk_RSHIFT( ylo - yhi, 8 - BIN_DIV_STEPS_A2NLSF_FIX ) ); 198 } 199 NLSF[ root_ix ] = (opus_int16)silk_min_32( silk_LSHIFT( (opus_int32)k, 8 ) + ffrac, silk_int16_MAX ); 200 201 silk_assert( NLSF[ root_ix ] >= 0 ); 202 203 root_ix++; /* Next root */ 204 if( root_ix >= d ) { 205 /* Found all roots */ 206 break; 207 } 208 /* Alternate pointer to polynomial */ 209 p = PQ[ root_ix & 1 ]; 210 211 /* Evaluate polynomial */ 212 xlo = silk_LSFCosTab_FIX_Q12[ k - 1 ]; /* Q12*/ 213 ylo = silk_LSHIFT( 1 - ( root_ix & 2 ), 12 ); 214 } else { 215 /* Increment loop counter */ 216 k++; 217 xlo = xhi; 218 ylo = yhi; 219 thr = 0; 220 221 if( k > LSF_COS_TAB_SZ_FIX ) { 222 i++; 223 if( i > MAX_ITERATIONS_A2NLSF_FIX ) { 224 /* Set NLSFs to white spectrum and exit */ 225 NLSF[ 0 ] = (opus_int16)silk_DIV32_16( 1 << 15, d + 1 ); 226 for( k = 1; k < d; k++ ) { 227 NLSF[ k ] = (opus_int16)silk_SMULBB( k + 1, NLSF[ 0 ] ); 228 } 229 return; 230 } 231 232 /* Error: Apply progressively more bandwidth expansion and run again */ 233 silk_bwexpander_32( a_Q16, d, 65536 - silk_SMULBB( 10 + i, i ) ); /* 10_Q16 = 0.00015*/ 234 235 silk_A2NLSF_init( a_Q16, P, Q, dd ); 236 p = P; /* Pointer to polynomial */ 237 xlo = silk_LSFCosTab_FIX_Q12[ 0 ]; /* Q12*/ 238 ylo = silk_A2NLSF_eval_poly( p, xlo, dd ); 239 if( ylo < 0 ) { 240 /* Set the first NLSF to zero and move on to the next */ 241 NLSF[ 0 ] = 0; 242 p = Q; /* Pointer to polynomial */ 243 ylo = silk_A2NLSF_eval_poly( p, xlo, dd ); 244 root_ix = 1; /* Index of current root */ 245 } else { 246 root_ix = 0; /* Index of current root */ 247 } 248 k = 1; /* Reset loop counter */ 249 } 250 } 251 } 252 } 253
