Function riffts1

src/core/_SoundPipe_FFT.cpp:3536–3593

}

static void riffts1(SPFLOAT * ioptr, int M, SPFLOAT * Utbl, int16_t * BRLow)
{
    /* Compute in-place real ifft on the rows of the input array    */
    /* data order as from rffts1                                    */
    /* INPUTS                                                       */
    /*   *ioptr = input data array in the following order           */
    /*   M = log2 of fft size                                       */
    /*   Re(x[0]), Re(x[N/2]), Re(x[1]), Im(x[1]),                  */
    /*   Re(x[2]), Im(x[2]), ... Re(x[N/2-1]), Im(x[N/2-1]).        */
    /*   *Utbl = cosine table                                       */
    /*   *BRLow = bit reversed counter table                        */
    /* OUTPUTS                                                      */
    /*   *ioptr = real output data array                            */

    SPFLOAT scale;
    int StageCnt;
    int NDiffU;

    scale = (SPFLOAT)(1.0 / (double) ((int) POW2(M)));
    M = M - 1;
    switch (M)
    {
        case -1:
            break;
        case 0:
            rifft1pt(ioptr, scale); /* a 2 pt fft */
            break;
        case 1:
            rifft2pt(ioptr, scale); /* a 4 pt fft */
            break;
        case 2:
            rifft4pt(ioptr, scale); /* an 8 pt fft */
            break;
        case 3:
            rifft8pt(ioptr, scale); /* a 16 pt fft */
            break;
        default:
            ifrstage(ioptr, M + 1, Utbl);
            /* bit reverse and first radix 2 stage */
            scbitrevR2(ioptr, M, BRLow, scale);
            StageCnt = (M - 1) / 3; /* number of radix 8 stages           */
            NDiffU = 2; /* one radix 2 stage already complete */
            if ((M - 1 - (StageCnt * 3)) == 1)
            {
                ibfR2(ioptr, M, NDiffU); /* 1 radix 2 stage */
                NDiffU *= 2;
            }
            if ((M - 1 - (StageCnt * 3)) == 2)
            {
                ibfR4(ioptr, M, NDiffU); /* 1 radix 4 stage */
                NDiffU *= 4;
            }
            if (M <= (int) MCACHE)
                ibfstages(ioptr, M, Utbl, 2, NDiffU, StageCnt); /*  RADIX 8 Stages */
            else
                ifftrecurs(ioptr, M, Utbl, 2, NDiffU, StageCnt); /* RADIX 8 Stages */
    }
}