freeswitch/libs/silk/src/SKP_Silk_resample_3_1.c

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/*                                                                      *
 * SKP_Silk_resample_3_1.c                                            *
 *                                                                      *
 * Upsamples by a factor 3                                              *
 *                                                                      *
 * Copyright 2008 (c), Skype Limited                                    *
 * Date: 081113                                                         *
 *                                                                      */
#include "SKP_Silk_SigProc_FIX.h"

#define IN_SUBFR_LEN_RESAMPLE_3_1       40

/* Resamples by a factor 3/1 */
void SKP_Silk_resample_3_1(
    SKP_int16           *out,       /* O:   Fs_high signal [inLen*3]        */
    SKP_int32           *S,         /* I/O: State vector   [7]              */
    const SKP_int16     *in,        /* I:   Fs_low signal  [inLen]          */
    const SKP_int32     inLen       /* I:   Input length                    */
)
{
    SKP_int     k, LSubFrameIn, LSubFrameOut;
    SKP_int32   out_tmp, idx, inLenTmp = inLen;
    SKP_int32   scratch00[    IN_SUBFR_LEN_RESAMPLE_3_1 ];
    SKP_int32   scratch0[ 3 * IN_SUBFR_LEN_RESAMPLE_3_1 ];
    SKP_int32   scratch1[ 3 * IN_SUBFR_LEN_RESAMPLE_3_1 ];
    
    /* Coefficients for 3-fold resampling */
    const SKP_int16 A30[ 2 ] = {  1773, 17818 };
    const SKP_int16 A31[ 2 ] = {  4942, 25677 };
    const SKP_int16 A32[ 2 ] = { 11786, 29304 };

    while( inLenTmp > 0 ) {
        LSubFrameIn  = SKP_min_int( IN_SUBFR_LEN_RESAMPLE_3_1, inLenTmp );
        LSubFrameOut = SKP_SMULBB( 3, LSubFrameIn );

        /* Convert Q15 -> Q25 */
        for( k = 0; k < LSubFrameIn; k++ ) {
            scratch00[k] = SKP_LSHIFT( (SKP_int32)in[ k ], 10 );
        }

        /* Allpass filtering */
        /* Scratch size: 2 * 3* LSubFrame * sizeof(SKP_int32) */
        SKP_Silk_allpass_int( scratch00, S + 1, A30[ 0 ], scratch1, LSubFrameIn );
        SKP_Silk_allpass_int( scratch1,  S + 2, A30[ 1 ], scratch0, LSubFrameIn );

        SKP_Silk_allpass_int( scratch00, S + 3, A31[ 0 ], scratch1, LSubFrameIn );
        SKP_Silk_allpass_int( scratch1,  S + 4, A31[ 1 ], scratch0 +     IN_SUBFR_LEN_RESAMPLE_3_1, LSubFrameIn );

        SKP_Silk_allpass_int( scratch00, S + 5, A32[ 0 ], scratch1, LSubFrameIn );
        SKP_Silk_allpass_int( scratch1,  S + 6, A32[ 1 ], scratch0 + 2 * IN_SUBFR_LEN_RESAMPLE_3_1, LSubFrameIn );

        /* Interleave three allpass outputs */
        for( k = 0; k < LSubFrameIn; k++ ) {
            idx = SKP_SMULBB( 3, k );
            scratch1[ idx     ] = scratch0[ k ];
            scratch1[ idx + 1 ] = scratch0[ k +     IN_SUBFR_LEN_RESAMPLE_3_1 ];
            scratch1[ idx + 2 ] = scratch0[ k + 2 * IN_SUBFR_LEN_RESAMPLE_3_1 ];
        }

        /* Low-pass filtering */
        SKP_Silk_lowpass_int( scratch1, S, scratch0, LSubFrameOut );

        /* Saturate and convert to SKP_int16 */
        for( k = 0; k < LSubFrameOut; k++ ) {
            out_tmp  = scratch0[ k ];
            out[ k ] = (SKP_int16) SKP_SAT16( SKP_RSHIFT_ROUND( out_tmp, 10 ) );
        }

        in       += LSubFrameIn;
        inLenTmp -= LSubFrameIn;
        out      += LSubFrameOut;
    }
}