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/*                                                                      *
 * SKP_Silk_LPC_synthesis_order16.c                                   *
 * Coefficients are in Q12                                              *
 *                                                                      *
 * 16th order AR filter                                                 *
 *                                                                      */
#include "SKP_Silk_SigProc_FIX.h"

/* 16th order AR filter */
void SKP_Silk_LPC_synthesis_order16(const SKP_int16 *in,          /* I:   excitation signal */
                                      const SKP_int16 *A_Q12,       /* I:   AR coefficients [16], between -8_Q0 and 8_Q0 */
                                      const SKP_int32 Gain_Q26,     /* I:   gain */
                                      SKP_int32 *S,                 /* I/O: state vector [16] */
                                      SKP_int16 *out,               /* O:   output signal */
                                      const SKP_int32 len           /* I:   signal length, must be multiple of 16 */
)
{
    SKP_int   k;
    SKP_int32 SA, SB, out32_Q10, out32;
    for( k = 0; k < len; k++ ) {
        /* unrolled loop: prolog */
        /* multiply-add two prediction coefficients per iteration */
        SA = S[ 15 ];
        SB = S[ 14 ];
        S[ 14 ] = SA;
        out32_Q10 = SKP_SMULWB(                  SA, A_Q12[ 0 ] );
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SB, A_Q12[ 1 ] );
        SA = S[ 13 ];
        S[ 13 ] = SB;

        /* unrolled loop: main loop */
        SB = S[ 12 ];
        S[ 12 ] = SA;
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SA, A_Q12[ 2 ] );
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SB, A_Q12[ 3 ] );
        SA = S[ 11 ];
        S[ 11 ] = SB;

        SB = S[ 10 ];
        S[ 10 ] = SA;
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SA, A_Q12[ 4 ] );
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SB, A_Q12[ 5 ] );
        SA = S[ 9 ];
        S[ 9 ] = SB;

        SB = S[ 8 ];
        S[ 8 ] = SA;
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SA, A_Q12[ 6 ] );
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SB, A_Q12[ 7 ] );
        SA = S[ 7 ];
        S[ 7 ] = SB;

        SB = S[ 6 ];
        S[ 6 ] = SA;
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SA, A_Q12[ 8 ] );
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SB, A_Q12[ 9 ] );
        SA = S[ 5 ];
        S[ 5 ] = SB;

        SB = S[ 4 ];
        S[ 4 ] = SA;
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SA, A_Q12[ 10 ] );
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SB, A_Q12[ 11 ] );
        SA = S[ 3 ];
        S[ 3 ] = SB;

        SB = S[ 2 ];
        S[ 2 ] = SA;
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SA, A_Q12[ 12 ] );
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SB, A_Q12[ 13 ] );
        SA = S[ 1 ];
        S[ 1 ] = SB;

        /* unrolled loop: epilog */
        SB = S[ 0 ];
        S[ 0 ] = SA;
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SA, A_Q12[ 14 ] );
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SB, A_Q12[ 15 ] );

        /* unrolled loop: end */
        /* apply gain to excitation signal and add to prediction */
        out32_Q10 = SKP_ADD_SAT32( out32_Q10, SKP_SMULWB( Gain_Q26, in[ k ] ) );

        /* scale to Q0 */
        out32 = SKP_RSHIFT_ROUND( out32_Q10, 10 );

        /* saturate output */
        out[ k ] = ( SKP_int16 )SKP_SAT16( out32 );

        /* move result into delay line */
        S[ 15 ] = SKP_LSHIFT_SAT32( out32_Q10, 4 );
    }
}
