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27
28 #ifdef HAVE_CONFIG_H
29 #include "config.h"
30 #endif
31
32 #include "SigProc_FIX.h"
33
34 /* Slower than schur(), but more accurate. */
35 /* Uses SMULL(), available on armv4 */
silk_schur64(opus_int32 rc_Q16[],const opus_int32 c[],opus_int32 order)36 opus_int32 silk_schur64( /* O returns residual energy */
37 opus_int32 rc_Q16[], /* O Reflection coefficients [order] Q16 */
38 const opus_int32 c[], /* I Correlations [order+1] */
39 opus_int32 order /* I Prediction order */
40 )
41 {
42 opus_int k, n;
43 opus_int32 C[ SILK_MAX_ORDER_LPC + 1 ][ 2 ];
44 opus_int32 Ctmp1_Q30, Ctmp2_Q30, rc_tmp_Q31;
45
46 silk_assert( order==6||order==8||order==10||order==12||order==14||order==16 );
47
48 /* Check for invalid input */
49 if( c[ 0 ] <= 0 ) {
50 silk_memset( rc_Q16, 0, order * sizeof( opus_int32 ) );
51 return 0;
52 }
53
54 for( k = 0; k < order + 1; k++ ) {
55 C[ k ][ 0 ] = C[ k ][ 1 ] = c[ k ];
56 }
57
58 for( k = 0; k < order; k++ ) {
59 /* Check that we won't be getting an unstable rc, otherwise stop here. */
60 if (silk_abs_int32(C[ k + 1 ][ 0 ]) >= C[ 0 ][ 1 ]) {
61 if ( C[ k + 1 ][ 0 ] > 0 ) {
62 rc_Q16[ k ] = -SILK_FIX_CONST( .99f, 16 );
63 } else {
64 rc_Q16[ k ] = SILK_FIX_CONST( .99f, 16 );
65 }
66 k++;
67 break;
68 }
69
70 /* Get reflection coefficient: divide two Q30 values and get result in Q31 */
71 rc_tmp_Q31 = silk_DIV32_varQ( -C[ k + 1 ][ 0 ], C[ 0 ][ 1 ], 31 );
72
73 /* Save the output */
74 rc_Q16[ k ] = silk_RSHIFT_ROUND( rc_tmp_Q31, 15 );
75
76 /* Update correlations */
77 for( n = 0; n < order - k; n++ ) {
78 Ctmp1_Q30 = C[ n + k + 1 ][ 0 ];
79 Ctmp2_Q30 = C[ n ][ 1 ];
80
81 /* Multiply and add the highest int32 */
82 C[ n + k + 1 ][ 0 ] = Ctmp1_Q30 + silk_SMMUL( silk_LSHIFT( Ctmp2_Q30, 1 ), rc_tmp_Q31 );
83 C[ n ][ 1 ] = Ctmp2_Q30 + silk_SMMUL( silk_LSHIFT( Ctmp1_Q30, 1 ), rc_tmp_Q31 );
84 }
85 }
86
87 for(; k < order; k++ ) {
88 rc_Q16[ k ] = 0;
89 }
90
91 return silk_max_32( 1, C[ 0 ][ 1 ] );
92 }
93