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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, Atmp, A_align_Q12[8], out32_Q10, out32;

    /* combine two A_Q12 values and ensure 32-bit alignment */
    for( k = 0; k < 8; k++ ) {
        A_align_Q12[k] = (((SKP_int32)A_Q12[ 2*k ]) & 0x0000ffff) | SKP_LSHIFT( (SKP_int32)A_Q12[ 2*k + 1 ], 16 );
    }

    /* S[] values are in Q14 */
    /* NOTE: the code below loads two int16 values in an int32, and multiplies each using the   */
    /* SMLAWB and SMLAWT instructions. On a big-endian CPU the two int16 variables would be     */
    /* loaded in reverse order and the code will give the wrong result. In that case swapping   */
    /* the SMLAWB and SMLAWT instructions should solve the problem.                             */
    for( k = 0; k < len; k++ ) {
        /* unrolled loop: prolog */
        /* multiply-add two prediction coefficients per iteration */
        SA = S[15];
        Atmp = A_align_Q12[0];
        SB = S[14];
        S[14] = SA;
        out32_Q10 = SKP_SMULWB(                  SA, Atmp );
        out32_Q10 = SKP_SMLAWT_ovflw( out32_Q10, SB, Atmp );
        SA = S[13];
        S[13] = SB;

        /* unrolled loop: main loop */
        Atmp = A_align_Q12[1];
        SB = S[12];
        S[12] = SA;
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SA, Atmp );
        out32_Q10 = SKP_SMLAWT_ovflw( out32_Q10, SB, Atmp );
        SA = S[11];
        S[11] = SB;

        Atmp = A_align_Q12[2];
        SB = S[10];
        S[10] = SA;
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SA, Atmp );
        out32_Q10 = SKP_SMLAWT_ovflw( out32_Q10, SB, Atmp );
        SA = S[9];
        S[9] = SB;

        Atmp = A_align_Q12[3];
        SB = S[8];
        S[8] = SA;
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SA, Atmp );
        out32_Q10 = SKP_SMLAWT_ovflw( out32_Q10, SB, Atmp );
        SA = S[7];
        S[7] = SB;

        Atmp = A_align_Q12[4];
        SB = S[6];
        S[6] = SA;
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SA, Atmp );
        out32_Q10 = SKP_SMLAWT_ovflw( out32_Q10, SB, Atmp );
        SA = S[5];
        S[5] = SB;

        Atmp = A_align_Q12[5];
        SB = S[4];
        S[4] = SA;
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SA, Atmp );
        out32_Q10 = SKP_SMLAWT_ovflw( out32_Q10, SB, Atmp );
        SA = S[3];
        S[3] = SB;

        Atmp = A_align_Q12[6];
        SB = S[2];
        S[2] = SA;
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SA, Atmp );
        out32_Q10 = SKP_SMLAWT_ovflw( out32_Q10, SB, Atmp );
        SA = S[1];
        S[1] = SB;

        /* unrolled loop: epilog */
        Atmp = A_align_Q12[7];
        SB = S[0];
        S[0] = SA;
        out32_Q10 = SKP_SMLAWB_ovflw( out32_Q10, SA, Atmp );
        out32_Q10 = SKP_SMLAWT_ovflw( out32_Q10, SB, Atmp );

        /* 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 );
    }
}


