• Lynne's avatar
    lavu/tx: implement 32 bit fixed point FFT and MDCT · e8f054b0
    Lynne authored
    Required minimal changes to the code so made sense to implement.
    FFT and MDCT tested, the output of both was properly rounded.
    Fun fact: the non-power-of-two fixed-point FFT and MDCT are the fastest ever
    non-power-of-two fixed-point FFT and MDCT written.
    This can replace the power of two integer MDCTs in aac and ac3 if the
    MIPS optimizations are ported across.
    Unfortunately the ac3 encoder uses a 16-bit fixed point forward transform,
    unlike the encoder which uses a 32bit inverse transform, so some modifications
    might be required there.
    
    The 3-point FFT is somewhat less accurate than it otherwise could be,
    having minor rounding errors with bigger transforms. However, this
    could be improved later, and the way its currently written is the way one
    would write assembly for it.
    Similar rounding errors can also be found throughout the power of two FFTs
    as well, though those are more difficult to correct.
    Despite this, the integer transforms are more than accurate enough.
    e8f054b0
tx.c 4.24 KB