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27
28 #ifdef HAVE_CONFIG_H
29 #include "config.h"
30 #endif
31
32 #include "SigProc_FIX.h"
33
34 /* Faster than schur64(), but much less accurate. */
35 /* uses SMLAWB(), requiring armv5E and higher. */
silk_schur(opus_int16 * rc_Q15,const opus_int32 * c,const opus_int32 order)36 opus_int32 silk_schur( /* O Returns residual energy */
37 opus_int16 *rc_Q15, /* O reflection coefficients [order] Q15 */
38 const opus_int32 *c, /* I correlations [order+1] */
39 const opus_int32 order /* I prediction order */
40 )
41 {
42 opus_int k, n, lz;
43 opus_int32 C[ SILK_MAX_ORDER_LPC + 1 ][ 2 ];
44 opus_int32 Ctmp1, Ctmp2, rc_tmp_Q15;
45
46 silk_assert( order==6||order==8||order==10||order==12||order==14||order==16 );
47
48 /* Get number of leading zeros */
49 lz = silk_CLZ32( c[ 0 ] );
50
51 /* Copy correlations and adjust level to Q30 */
52 if( lz < 2 ) {
53 /* lz must be 1, so shift one to the right */
54 for( k = 0; k < order + 1; k++ ) {
55 C[ k ][ 0 ] = C[ k ][ 1 ] = silk_RSHIFT( c[ k ], 1 );
56 }
57 } else if( lz > 2 ) {
58 /* Shift to the left */
59 lz -= 2;
60 for( k = 0; k < order + 1; k++ ) {
61 C[ k ][ 0 ] = C[ k ][ 1 ] = silk_LSHIFT( c[ k ], lz );
62 }
63 } else {
64 /* No need to shift */
65 for( k = 0; k < order + 1; k++ ) {
66 C[ k ][ 0 ] = C[ k ][ 1 ] = c[ k ];
67 }
68 }
69
70 for( k = 0; k < order; k++ ) {
71 /* Check that we won't be getting an unstable rc, otherwise stop here. */
72 if (silk_abs_int32(C[ k + 1 ][ 0 ]) >= C[ 0 ][ 1 ]) {
73 if ( C[ k + 1 ][ 0 ] > 0 ) {
74 rc_Q15[ k ] = -SILK_FIX_CONST( .99f, 15 );
75 } else {
76 rc_Q15[ k ] = SILK_FIX_CONST( .99f, 15 );
77 }
78 k++;
79 break;
80 }
81
82 /* Get reflection coefficient */
83 rc_tmp_Q15 = -silk_DIV32_16( C[ k + 1 ][ 0 ], silk_max_32( silk_RSHIFT( C[ 0 ][ 1 ], 15 ), 1 ) );
84
85 /* Clip (shouldn't happen for properly conditioned inputs) */
86 rc_tmp_Q15 = silk_SAT16( rc_tmp_Q15 );
87
88 /* Store */
89 rc_Q15[ k ] = (opus_int16)rc_tmp_Q15;
90
91 /* Update correlations */
92 for( n = 0; n < order - k; n++ ) {
93 Ctmp1 = C[ n + k + 1 ][ 0 ];
94 Ctmp2 = C[ n ][ 1 ];
95 C[ n + k + 1 ][ 0 ] = silk_SMLAWB( Ctmp1, silk_LSHIFT( Ctmp2, 1 ), rc_tmp_Q15 );
96 C[ n ][ 1 ] = silk_SMLAWB( Ctmp2, silk_LSHIFT( Ctmp1, 1 ), rc_tmp_Q15 );
97 }
98 }
99
100 for(; k < order; k++ ) {
101 rc_Q15[ k ] = 0;
102 }
103
104 /* return residual energy */
105 return silk_max_32( 1, C[ 0 ][ 1 ] );
106 }
107