• Timothy B. Terriberry's avatar
    Add 4-tap version of 2nd-pass ARMv6 MC filter. · 18dc92fd
    Timothy B. Terriberry authored
    The existing code applied a 6-tap filter with 0's on either end.
    We're already paying the branch penalty to avoid computing the two
     extra columns needed as input to this filter.
    We might as well save time computing the filter as well.
    This reduces the inner loop from 21 instructions to 16, the number
     of loads per iteration from 4 to 1, and the number of multiplies
     from 7 to 4.
    The gain in overall decoding performance, however, is small (less
     than 1%).
    
    This change also means we now valgrind clean on ARMv6, which is
     its real purpose.
    The errors reported here were valgrind's fault (it does not detect
     that 0 times an uninitialized value is initialized), but Julian
     Seward says it would slow down valgrind considerably to make such
     checks.
    Speeding up libvpx rather, even by a small amount, seems a much
     better idea if only to enable proper valgrind checking of the
     rest of the codec.
    
    Change-Id: Ifb376ea195e086b60f61daf1097d8910c4d8ff16
    18dc92fd