A.5.234 PMAXUB: Packed Unsigned Integer Byte Maximum
PMAXUB mm1,mm2/m64 ; 0F DE /r [KATMAI,MMX]
PMAXUB xmm1,xmm2/m128 ; 66 0F DE /r [WILLAMETTE,SSE2]
PMAXUB compares each pair of bytes in the two source operands, and for
each pair it stores the maximum value in the destination register.