freeswitch/libs/silk/src/SKP_Silk_resampler_private_up4.c

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/*                                                                      *
 * SKP_Silk_resampler_private_up4.c                                   *
 *                                                                      *
 * Upsample by a factor 4, low quality                                  *
 *                                                                      *
 * Copyright 2010 (c), Skype Limited                                    *
 *                                                                      */

#include "SKP_Silk_SigProc_FIX.h"
#include "SKP_Silk_resampler_private.h"

/* Upsample by a factor 4, Note: very low quality, only use with output sampling rates above 96 kHz. */
void SKP_Silk_resampler_private_up4(
    SKP_int32                       *S,             /* I/O: State vector [ 2 ]                      */
    SKP_int16                       *out,           /* O:   Output signal [ 4 * len ]               */
    const SKP_int16                 *in,            /* I:   Input signal [ len ]                    */
    SKP_int32                       len             /* I:   Number of INPUT samples                 */
)
{
    SKP_int32 k;
    SKP_int32 in32, out32, Y, X;
    SKP_int16 out16;

    SKP_assert( SKP_Silk_resampler_up2_lq_0 > 0 );
    SKP_assert( SKP_Silk_resampler_up2_lq_1 < 0 );

    /* Internal variables and state are in Q10 format */
    for( k = 0; k < len; k++ ) {
        /* Convert to Q10 */
        in32 = SKP_LSHIFT( (SKP_int32)in[ k ], 10 );

        /* All-pass section for even output sample */
        Y      = SKP_SUB32( in32, S[ 0 ] );
        X      = SKP_SMULWB( Y, SKP_Silk_resampler_up2_lq_0 );
        out32  = SKP_ADD32( S[ 0 ], X );
        S[ 0 ] = SKP_ADD32( in32, X );

        /* Convert back to int16 and store to output */
        out16 = (SKP_int16)SKP_SAT16( SKP_RSHIFT_ROUND( out32, 10 ) );
        out[ 4 * k ]     = out16;
        out[ 4 * k + 1 ] = out16;

        /* All-pass section for odd output sample */
        Y      = SKP_SUB32( in32, S[ 1 ] );
        X      = SKP_SMLAWB( Y, Y, SKP_Silk_resampler_up2_lq_1 );
        out32  = SKP_ADD32( S[ 1 ], X );
        S[ 1 ] = SKP_ADD32( in32, X );

        /* Convert back to int16 and store to output */
        out16 = (SKP_int16)SKP_SAT16( SKP_RSHIFT_ROUND( out32, 10 ) );
        out[ 4 * k + 2 ] = out16;
        out[ 4 * k + 3 ] = out16;
    }
}