A.5.145 MASKMOVDQU: Byte Mask Write
MASKMOVDQU xmm1,xmm2 ; 66 0F F7 /r [WILLAMETTE,SSE2]
MASKMOVDQU stores data from xmm1 to the location specified by ES:(E)DI.
The size of the store depends on the address-size attribute. The most
significant bit in each byte of the mask register xmm2 is used to
selectively write the data (0 = no write, 1 = write) on a per-byte
basis.