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#ifdef HAVE_CONFIG_H

#include "config.h"

#endif

#include "SigProc_FLP.h"

#include "tuning_parameters.h"

#include "define.h"

#define MAX_FRAME_SIZE              384 /* subfr_length * nb_subfr = ( 0.005 * 16000 + 16 ) * 4 = 384*/

/* Compute reflection coefficients from input signal */

silk_float silk_burg_modified_FLP(          /* O    returns residual energy                                     */

    silk_float          A[],                /* O    prediction coefficients (length order)                      */

    const silk_float    x[],                /* I    input signal, length: nb_subfr*(D+L_sub)                    */

    const silk_float    minInvGain,         /* I    minimum inverse prediction gain                             */

    const opus_int      subfr_length,       /* I    input signal subframe length (incl. D preceding samples)    */

    const opus_int      nb_subfr,           /* I    number of subframes stacked in x                            */

    const opus_int      D,                  /* I    order                                                       */

    int                 arch

)

{

    opus_int         k, n, s, reached_max_gain;

    double           C0, invGain, num, nrg_f, nrg_b, rc, Atmp, tmp1, tmp2;

    const silk_float *x_ptr;

    double           C_first_row[ SILK_MAX_ORDER_LPC ], C_last_row[ SILK_MAX_ORDER_LPC ];

    double           CAf[ SILK_MAX_ORDER_LPC + 1 ], CAb[ SILK_MAX_ORDER_LPC + 1 ];

    double           Af[ SILK_MAX_ORDER_LPC ];

    celt_assert( subfr_length * nb_subfr <= MAX_FRAME_SIZE );

    /* Compute autocorrelations, added over subframes */

    C0 = silk_energy_FLP( x, nb_subfr * subfr_length );

    silk_memset( C_first_row, 0, SILK_MAX_ORDER_LPC * sizeof( double ) );

    for( s = 0; s < nb_subfr; s++ ) {

        x_ptr = x + s * subfr_length;

        for( n = 1; n < D + 1; n++ ) {

            C_first_row[ n - 1 ] += silk_inner_product_FLP( x_ptr, x_ptr + n, subfr_length - n, arch );

        }

    }

    silk_memcpy( C_last_row, C_first_row, SILK_MAX_ORDER_LPC * sizeof( double ) );

    /* Initialize */

    CAb[ 0 ] = CAf[ 0 ] = C0 + FIND_LPC_COND_FAC * C0 + 1e-9f;

    invGain = 1.0f;

    reached_max_gain = 0;

    for( n = 0; n < D; n++ ) {

        /* Update first row of correlation matrix (without first element) */

        /* Update last row of correlation matrix (without last element, stored in reversed order) */

        /* Update C * Af */

        /* Update C * flipud(Af) (stored in reversed order) */

        for( s = 0; s < nb_subfr; s++ ) {

            x_ptr = x + s * subfr_length;

            tmp1 = x_ptr[ n ];

            tmp2 = x_ptr[ subfr_length - n - 1 ];

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

                C_first_row[ k ] -= x_ptr[ n ] * x_ptr[ n - k - 1 ];

                C_last_row[ k ]  -= x_ptr[ subfr_length - n - 1 ] * x_ptr[ subfr_length - n + k ];

                Atmp = Af[ k ];

                tmp1 += x_ptr[ n - k - 1 ] * Atmp;

                tmp2 += x_ptr[ subfr_length - n + k ] * Atmp;

            }

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

                CAf[ k ] -= tmp1 * x_ptr[ n - k ];

                CAb[ k ] -= tmp2 * x_ptr[ subfr_length - n + k - 1 ];

            }

        }

        tmp1 = C_first_row[ n ];

        tmp2 = C_last_row[ n ];

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

            Atmp = Af[ k ];

            tmp1 += C_last_row[  n - k - 1 ] * Atmp;

            tmp2 += C_first_row[ n - k - 1 ] * Atmp;

        }

        CAf[ n + 1 ] = tmp1;

        CAb[ n + 1 ] = tmp2;

        /* Calculate nominator and denominator for the next order reflection (parcor) coefficient */

        num = CAb[ n + 1 ];

        nrg_b = CAb[ 0 ];

        nrg_f = CAf[ 0 ];

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

            Atmp = Af[ k ];

            num   += CAb[ n - k ] * Atmp;

            nrg_b += CAb[ k + 1 ] * Atmp;

            nrg_f += CAf[ k + 1 ] * Atmp;

        }

        silk_assert( nrg_f > 0.0 );

        silk_assert( nrg_b > 0.0 );

        /* Calculate the next order reflection (parcor) coefficient */

        rc = -2.0 * num / ( nrg_f + nrg_b );

        silk_assert( rc > -1.0 && rc < 1.0 );

        /* Update inverse prediction gain */

        tmp1 = invGain * ( 1.0 - rc * rc );

        if( tmp1 <= minInvGain ) {

            /* Max prediction gain exceeded; set reflection coefficient such that max prediction gain is exactly hit */

            rc = sqrt( 1.0 - minInvGain / invGain );

            if( num > 0 ) {

                /* Ensure adjusted reflection coefficients has the original sign */

                rc = -rc;

            }

            invGain = minInvGain;

            reached_max_gain = 1;

        } else {

            invGain = tmp1;

        }

        /* Update the AR coefficients */

        for( k = 0; k < (n + 1) >> 1; k++ ) {

            tmp1 = Af[ k ];

            tmp2 = Af[ n - k - 1 ];

            Af[ k ]         = tmp1 + rc * tmp2;

            Af[ n - k - 1 ] = tmp2 + rc * tmp1;

        }

        Af[ n ] = rc;

        if( reached_max_gain ) {

            /* Reached max prediction gain; set remaining coefficients to zero and exit loop */

            for( k = n + 1; k < D; k++ ) {

                Af[ k ] = 0.0;

            }

            break;

        }

        /* Update C * Af and C * Ab */

        for( k = 0; k <= n + 1; k++ ) {

            tmp1 = CAf[ k ];

            CAf[ k ]          += rc * CAb[ n - k + 1 ];

            CAb[ n - k + 1  ] += rc * tmp1;

        }

    }

    if( reached_max_gain ) {

        /* Convert to silk_float */

        for( k = 0; k < D; k++ ) {

            A[ k ] = (silk_float)( -Af[ k ] );

        }

        /* Subtract energy of preceding samples from C0 */

        for( s = 0; s < nb_subfr; s++ ) {

            C0 -= silk_energy_FLP( x + s * subfr_length, D );

        }

        /* Approximate residual energy */

        nrg_f = C0 * invGain;

    } else {

        /* Compute residual energy and store coefficients as silk_float */

        nrg_f = CAf[ 0 ];

        tmp1 = 1.0;

        for( k = 0; k < D; k++ ) {

            Atmp = Af[ k ];

            nrg_f += CAf[ k + 1 ] * Atmp;

            tmp1  += Atmp * Atmp;

            A[ k ] = (silk_float)(-Atmp);

        }

        nrg_f -= FIND_LPC_COND_FAC * C0 * tmp1;

    }

    /* Return residual energy */

    return (silk_float)nrg_f;

}