Those are mostly used in codecs older than H.264, eg MPEG-2.

put16 versions:
      mmx  mmx2  sse2
x2:  1888  1185   552
y2:  1778  1092   510

avg16 xy2: 3509(mmx2) -> 2169(sse2)
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>