ref: 6f9a028cad836b8f41f479d244be849fc16e48b8
dir: /src_SigProc_FLP/SKP_Silk_decimate2_coarsest_FLP.c/
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/* *
* SKP_Silk_decimate2_coarsest.c *
* *
* downsample by a factor 2, coarsest *
* *
* Copyright 2006 (c), Camino Networks *
* Date: 060221 *
* */
#include "SKP_Silk_SigProc_FLP.h"
/* coefficients for coarsest 2-fold resampling */
/* note that these differ from the interpolator with the same filter orders! */
static float A20cst_FLP[ 1 ] = {0.289001464843750f};
static float A21cst_FLP[ 1 ] = {0.780487060546875f};
/* downsample by a factor 2, coarsest */
void SKP_Silk_decimate2_coarsest_FLP(
const SKP_float *in, /* I: 16 kHz signal [2*len] */
SKP_float *S, /* I/O: state vector [2] */
SKP_float *out, /* O: 8 kHz signal [len] */
SKP_float *scratch, /* I: scratch memory [3*len] */
const SKP_int32 len /* I: number of OUTPUT samples */
)
{
SKP_int32 k;
/* de-interleave allpass inputs */
for ( k = 0; k < len; k++ ) {
scratch[ k ] = in[ 2 * k + 0 ];
scratch[ k + len ] = in[ 2 * k + 1 ];
}
/* allpass filters */
SKP_Silk_allpass_int_FLP( scratch, S + 0, A21cst_FLP[ 0 ], scratch + 2 * len, len );
SKP_Silk_allpass_int_FLP( scratch + len, S + 1, A20cst_FLP[ 0 ], scratch, len );
/* add two allpass outputs */
for ( k = 0; k < len; k++ ) {
out[ k ] = 0.5f * ( scratch[ k ] + scratch[ k + 2 * len ] );
}
}