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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 ] );

}