PACKSSDW        Pack Doublewords into Words (Signed with Saturation)

PACKSSDW destination, source                         CPU: MMX

        Logic
        mm(15..0)  <- SaturateSignedDwordToSignedWord mm(31..0)
        mm(31..16) <- SaturateSignedDwordToSignedWord mm(63..32)
        mm(47..32) <- SaturateSignedDwordToSignedWord mm/m64(31..0)
        mm(63..48) <- SaturateSignedDwordToSignedWord mm/m64(63..32)

    PACKSSDW packs two signed doublewords from the source operand and
    two signed doublewords from the destination operand into four signed
    words in the destination register.
    If the signed value of a doubleword is larger or smaller than the
    range of a signed word, the value is saturated (in the case of an
    overflow to 7FFFh, and in the case of an underflow to 8000h).

    The destination operand is an MMX register. The source operand can
    either be an MMX register or a 64-bit memory operand. 


    Opcode      Format
    0F 6B /r    PACKSSDW mm, mm/m64