[XviD-devel] Are dequant_h263_intra and dequant_mpeg_intra interchangeable?

[Greg Handi]

In playing around with trying to merge things to see where I could get
better speed (for a RISC DSP) by combining methods I tried merging the
dequant_mpeg_intra method with the idct code (and then not calling idct
seperately afterwards of course).  Just for fun I removed the logic to
test for which dequant method to use (since I had only made a combined
version for mpeg) and just used mpeg and then played a file that used
h263 to see what it would look like using mpeg instead and much to my
surprise it still looked correct.  I would have thought that they were
not interchangeable but it seems to work, can anyone enlighten me on
why this is?  I have not written a test to do a binary comparison of
the output of an individual frame but to my eyes the video seems to
look fine...

Another question about combining operations for optimization, it made
sense for me to create two versions of the idct and combine them, as
apropriate, with the transfer_16to8copy and transfer_16to8add
respectively to eliminate extra memory accesses and some scaling
shifts, is this something that might be desireable to be done to the
main tree?  I'm not sure if I could write a proper patch for all the
various assembly versions but I'm wondering if one would even be
desireable?  Or would this be an inappropriate change to make?

Thank-you

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