• Jingning Han's avatar
    Butterfly ADST based hybrid transform · d15e1da4
    Jingning Han authored
    Refactor the 8x8 inverse hybrid transform. It is now consistent
    with the new inverse DCT. Overall performance loss (due to the
    use of this variant ADST, and the rounding errors in the butterfly
    implementation) for std-hd is -0.02.
    Fixed BUILD warning.
    Devise a variant of the original ADST, which allows butterfly
    computation structure. This new transform has kernel of the
    form: sin((2k+1)*(2n+1) / (4N)). One of its butterfly structures
    using floating-point multiplications was reported in Z. Wang,
    "Fast algorithms for the discrete W transform and for the discrete
    Fourier transform", IEEE Trans. on ASSP, 1984.
    This patch includes the butterfly implementation of the inverse
    ADST/DCT hybrid transform of dimension 8x8.
    Change-Id: I3533cb715f749343a80b9087ce34b3e776d1581d