MMX instruction to pack signed double words into signed words.
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 2 original double words of the destination register, packed down to words.
Dword values over 32767 are
clamped to 32767; dword values under -32768 are clamped to -32768. The low 32 bits of the destination register are filled in the same fashion, but with the source words from the source
operand.
Compare
PACKSSWB,
PACKUSDW.