opus/silk/fixed/schur_FIX.c

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#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "SigProc_FIX.h"

/* Faster than schur64(), but much less accurate.                       */
/* uses SMLAWB(), requiring armv5E and higher.                          */
opus_int32 silk_schur(                              /* O    Returns residual energy                                     */
    opus_int16                  *rc_Q15,            /* O    reflection coefficients [order] Q15                         */
    const opus_int32            *c,                 /* I    correlations [order+1]                                      */
    const opus_int32            order               /* I    prediction order                                            */
)
{
    opus_int        k, n, lz;
    opus_int32    C[ SILK_MAX_ORDER_LPC + 1 ][ 2 ];
    opus_int32    Ctmp1, Ctmp2, rc_tmp_Q15;

    celt_assert( order >= 0 && order <= SILK_MAX_ORDER_LPC );

    /* Get number of leading zeros */
    lz = silk_CLZ32( c[ 0 ] );

    /* Copy correlations and adjust level to Q30 */
    k = 0;
    if( lz < 2 ) {
        /* lz must be 1, so shift one to the right */
        do {
            C[ k ][ 0 ] = C[ k ][ 1 ] = silk_RSHIFT( c[ k ], 1 );
        } while( ++k <= order );
    } else if( lz > 2 ) {
        /* Shift to the left */
        lz -= 2;
        do {
            C[ k ][ 0 ] = C[ k ][ 1 ] = silk_LSHIFT( c[ k ], lz );
        } while( ++k <= order );
    } else {
        /* No need to shift */
        do {
            C[ k ][ 0 ] = C[ k ][ 1 ] = c[ k ];
        } while( ++k <= order );
    }

    for( k = 0; k < order; k++ ) {
        /* Check that we won't be getting an unstable rc, otherwise stop here. */
        if (silk_abs_int32(C[ k + 1 ][ 0 ]) >= C[ 0 ][ 1 ]) {
           if ( C[ k + 1 ][ 0 ] > 0 ) {
              rc_Q15[ k ] = -SILK_FIX_CONST( .99f, 15 );
           } else {
              rc_Q15[ k ] = SILK_FIX_CONST( .99f, 15 );
           }
           k++;
           break;
        }

        /* Get reflection coefficient */
        rc_tmp_Q15 = -silk_DIV32_16( C[ k + 1 ][ 0 ], silk_max_32( silk_RSHIFT( C[ 0 ][ 1 ], 15 ), 1 ) );

        /* Clip (shouldn't happen for properly conditioned inputs) */
        rc_tmp_Q15 = silk_SAT16( rc_tmp_Q15 );

        /* Store */
        rc_Q15[ k ] = (opus_int16)rc_tmp_Q15;

        /* Update correlations */
        for( n = 0; n < order - k; n++ ) {
            Ctmp1 = C[ n + k + 1 ][ 0 ];
            Ctmp2 = C[ n ][ 1 ];
            C[ n + k + 1 ][ 0 ] = silk_SMLAWB( Ctmp1, silk_LSHIFT( Ctmp2, 1 ), rc_tmp_Q15 );
            C[ n ][ 1 ]         = silk_SMLAWB( Ctmp2, silk_LSHIFT( Ctmp1, 1 ), rc_tmp_Q15 );
        }
    }

    for(; k < order; k++ ) {
       rc_Q15[ k ] = 0;
    }

    /* return residual energy */
    return silk_max_32( 1, C[ 0 ][ 1 ] );
}