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#ifdef HAVE_CONFIG_H

#include "config.h"

#endif

#include "SigProc_FIX.h"

/* Slower than schur(), but more accurate.                              */

/* Uses SMULL(), available on armv4                                     */

opus_int32 silk_schur64(                            /* O    returns residual energy                                     */

    opus_int32                  rc_Q16[],           /* O    Reflection coefficients [order] Q16                         */

    const opus_int32            c[],                /* I    Correlations [order+1]                                      */

    opus_int32                  order               /* I    Prediction order                                            */

)

{

    opus_int   k, n;

    opus_int32 C[ SILK_MAX_ORDER_LPC + 1 ][ 2 ];

    opus_int32 Ctmp1_Q30, Ctmp2_Q30, rc_tmp_Q31;

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

    /* Check for invalid input */

    if( c[ 0 ] <= 0 ) {

        silk_memset( rc_Q16, 0, order * sizeof( opus_int32 ) );

        return 0;

    }

    k = 0;

    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_Q16[ k ] = -SILK_FIX_CONST( .99f, 16 );

           } else {

              rc_Q16[ k ] = SILK_FIX_CONST( .99f, 16 );

           }

           k++;

           break;

        }

        /* Get reflection coefficient: divide two Q30 values and get result in Q31 */

        rc_tmp_Q31 = silk_DIV32_varQ( -C[ k + 1 ][ 0 ], C[ 0 ][ 1 ], 31 );

        /* Save the output */

        rc_Q16[ k ] = silk_RSHIFT_ROUND( rc_tmp_Q31, 15 );

        /* Update correlations */

        for( n = 0; n < order - k; n++ ) {

            Ctmp1_Q30 = C[ n + k + 1 ][ 0 ];

            Ctmp2_Q30 = C[ n ][ 1 ];

            /* Multiply and add the highest int32 */

            C[ n + k + 1 ][ 0 ] = Ctmp1_Q30 + silk_SMMUL( silk_LSHIFT( Ctmp2_Q30, 1 ), rc_tmp_Q31 );

            C[ n ][ 1 ]         = Ctmp2_Q30 + silk_SMMUL( silk_LSHIFT( Ctmp1_Q30, 1 ), rc_tmp_Q31 );

        }

    }

    for(; k < order; k++ ) {

       rc_Q16[ k ] = 0;

    }

    return silk_max_32( 1, C[ 0 ][ 1 ] );

}