MMX instruction to pack signed words into unsigned bytes.
Takes either two MMX
registers or an MMX register (source) and a
64 bit memory location (destination) as
operands.
The high 32 bits of the destination register are filled with the 4 original words of the destination register, packed down to bytes. Word values over 255 are
clamped to 255; negative word values are clamped to 0. The low 32 bits of the destination register are filled in the same fashion, but with the source words from the source
operand.
Compare
PACKUSDW,
PACKSSWB.