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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.                          */
36opus_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