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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(..) */
silk_NLSF2A_find_poly(opus_int32 * out,const opus_int32 * cLSF,opus_int dd)44 static OPUS_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 */
silk_NLSF2A(opus_int16 * a_Q12,const opus_int16 * NLSF,const opus_int d)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