• Yaowu Xu's avatar
    A fix point implementation of 32x32 idct · 5149d7f7
    Yaowu Xu authored
    This commit changes the 32x32 idct to use integer only. The algorithm
    was taken directly from "A Fast Computational Algorithm for the
    Discrete Cosine Tranform" by W. Chen, et al., which was published in
    IEEE Transaction on Communication Vol. Com.-25 No. 9, 1977. The signal
    flow graph in the original paper is for a 32 point forward dct, the
    current implementation of inverse DCT was done by follow the graph in
    reversed direction.
    With this implementation, the 32 point inverse dct contains a 16 point
    inverse dct in its even portion, similarly the 16 point idct further
    contains 8 point and 4 point inverse dcts.
    As of patch 4, encoding tests showed there is no compression loss when
    compared against the floating point baseline. Numbers even showed very
    small postives. (cif: .01%, std-hd: .05%).
    Change-Id: I2d2d17a424b0b04b42422ef33ec53f5802b0f378