/***********************************************************************

Copyright (c) 2013, Koen Vos. All rights reserved.

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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"

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***********************************************************************/

#ifdef HAVE_CONFIG_H

#include "config.h"

#endif

#include "SigProc_FIX.h"

/* Convert int32 coefficients to int16 coefs and make sure there's no wrap-around.

   This logic is reused in _celt_lpc(). Any bug fixes should also be applied there. */

void silk_LPC_fit(

    opus_int16                  *a_QOUT,            /* O    Output signal                                               */

    opus_int32                    *a_QIN,             /* I/O  Input signal                                                */

    const opus_int              QOUT,               /* I    Input Q domain                                              */

    const opus_int              QIN,                /* I    Input Q domain                                              */

    const opus_int              d                   /* I    Filter order                                                */

)

{

    opus_int    i, k, idx = 0;

    opus_int32    maxabs, absval, chirp_Q16;

    /* Limit the maximum absolute value of the prediction coefficients, so that they'll fit in int16 */

    for( i = 0; i < 10; i++ ) {

        /* Find maximum absolute value and its index */

        maxabs = 0;

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

            absval = silk_abs( a_QIN[k] );

            if( absval > maxabs ) {

                maxabs = absval;

                idx    = k;

            }

        }

        maxabs = silk_RSHIFT_ROUND( maxabs, QIN - QOUT );

        if( maxabs > silk_int16_MAX ) {

            /* Reduce magnitude of prediction coefficients */

            maxabs = silk_min( maxabs, 163838 );  /* ( silk_int32_MAX >> 14 ) + silk_int16_MAX = 163838 */

            chirp_Q16 = SILK_FIX_CONST( 0.999, 16 ) - silk_DIV32( silk_LSHIFT( maxabs - silk_int16_MAX, 14 ),

                                        silk_RSHIFT32( silk_MUL( maxabs, idx + 1), 2 ) );

            silk_bwexpander_32( a_QIN, d, chirp_Q16 );

        } else {

            break;

        }

    }

    if( i == 10 ) {

        /* Reached the last iteration, clip the coefficients */

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

            a_QOUT[ k ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( a_QIN[ k ], QIN - QOUT ) );

            a_QIN[ k ] = silk_LSHIFT( (opus_int32)a_QOUT[ k ], QIN - QOUT );

        }

    } else {

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

            a_QOUT[ k ] = (opus_int16)silk_RSHIFT_ROUND( a_QIN[ k ], QIN - QOUT );

        }

    }

}