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/*                                                                      *
 * SKP_Silk_lowpass_short.c                                           *
 *                                                                      *
 * First order low-pass filter, with input as SKP_int16, running at     *
 * 48 kHz                                                               *
 *                                                                      *
 * Copyright 2006 (c), Skype Limited                                    *
 * Date: 060221                                                         *
 *                                                                      */
#include "SKP_Silk_SigProc_FIX.h"


/* First order low-pass filter, with input as SKP_int16, running at 48 kHz   */
void SKP_Silk_lowpass_short(
    const SKP_int16          *in,        /* I:   Q15 48 kHz signal; [len]    */
    SKP_int32                *S,         /* I/O: Q25 state; length = 1       */
    SKP_int32                *out,       /* O:   Q25 48 kHz signal; [len]    */
    const SKP_int32          len         /* O:   Signal length               */
)
{
    SKP_int        k;
    SKP_int32    in_tmp, out_tmp, state;
    
    state = S[ 0 ];
    for( k = 0; k < len; k++ ) {    
        in_tmp   = SKP_MUL( 768, (SKP_int32)in[k] );    /* multiply by 0.75, going from Q15 to Q25 */
        out_tmp  = state + in_tmp;                      /* zero at nyquist                         */
        state    = in_tmp - SKP_RSHIFT( out_tmp, 1 );   /* pole                                    */
        out[ k ] = out_tmp;
    }
    S[ 0 ] = state;
}


