packusqd (saturated clamp from unsigned long long to unsigned long),
packssqud (saturated clamp from signed long long to unsigned long):

There is a condition for unsigned long long inputs, range is “only” [0x0000000000000000, 0x7FFFFFFFFFFF].
There is a no condition for signed long long inputs.

// from-scratch, no helper available

    /* -1 */
    pcmpeqd	mm6, mm6

    /* x >> 32 > -1 */
    movq	mm4, mmc0
    movq	mm5, mm2

    /* no psraq/pshufd/pshufw available,
     * duplicate ((x >> 32) | x) */
    punpckhdq	mm4, mmc0
    punpckhdq	mm5, mm2

    pcmpgtd	mm4, mm6
    pcmpgtd	mm5, mm6

    pand	mmc0, mm4
    pand	mm2, mm5

    /* 0 */
    pxor	mm7, mm7

    /* x >> 32 == 0 */
    movq	mm4, mmc0
    movq	mm5, mm2

    /* no psraq/pshufd/pshufw available,
     * duplicate ((x >> 32) | x) */
    punpckhdq	mm4, mmc0
    punpckhdq	mm5, mm2

    pcmpeqd	mm4, mm7
    pcmpeqd	mm5, mm7

    pand	mmc0, mm4
    pand	mm2, mm5

    /* 0xFFFFFFFF */
    pandn	mm4, mm6
    pandn	mm5, mm6

    por		mmc0, mm4
    por		mm2, mm5

    punpckldq	mmc0, mm2