ref: 2e7feb51249b620d9b441fdb88699cfc7560f7e8
dir: /silk/silk_resampler_private_down4.c/
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#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "silk_SigProc_FIX.h"
#include "silk_resampler_private.h"
/* Downsample by a factor 4. Note: very low quality, only use with input sampling rates above 96 kHz. */
void silk_resampler_private_down4(
opus_int32 *S, /* I/O: State vector [ 2 ] */
opus_int16 *out, /* O: Output signal [ floor(len/2) ] */
const opus_int16 *in, /* I: Input signal [ len ] */
opus_int32 inLen /* I: Number of input samples */
)
{
opus_int32 k, len4 = SKP_RSHIFT32( inLen, 2 );
opus_int32 in32, out32, Y, X;
SKP_assert( silk_resampler_down2_0 > 0 );
SKP_assert( silk_resampler_down2_1 < 0 );
/* Internal variables and state are in Q10 format */
for( k = 0; k < len4; k++ ) {
/* Add two input samples and convert to Q10 */
in32 = SKP_LSHIFT( SKP_ADD32( (opus_int32)in[ 4 * k ], (opus_int32)in[ 4 * k + 1 ] ), 9 );
/* All-pass section for even input sample */
Y = SKP_SUB32( in32, S[ 0 ] );
X = SKP_SMLAWB( Y, Y, silk_resampler_down2_1 );
out32 = SKP_ADD32( S[ 0 ], X );
S[ 0 ] = SKP_ADD32( in32, X );
/* Add two input samples and convert to Q10 */
in32 = SKP_LSHIFT( SKP_ADD32( (opus_int32)in[ 4 * k + 2 ], (opus_int32)in[ 4 * k + 3 ] ), 9 );
/* All-pass section for odd input sample */
Y = SKP_SUB32( in32, S[ 1 ] );
X = SKP_SMULWB( Y, silk_resampler_down2_0 );
out32 = SKP_ADD32( out32, S[ 1 ] );
out32 = SKP_ADD32( out32, X );
S[ 1 ] = SKP_ADD32( in32, X );
/* Add, convert back to int16 and store to output */
out[ k ] = (opus_int16)SKP_SAT16( SKP_RSHIFT_ROUND( out32, 11 ) );
}
}