// after the first two lower 64 bit limb adds, but before either
// high 64 bit limbs are added.
//
// This is what happened on PPC64 when compiling
// crypto/internal/edwards25519/field.feMulGeneric.
func Add64MultipleChains(a, b, c, d [2]uint64) {
	var cx, d1, d2 uint64
	a1, a2 := a[0], a[1]
	b1, b2 := b[0], b[1]
	c1, c2 := c[0], c[1]

	// ppc64x: "ADDC\tR\\d+,", -"ADDE", -"MOVD\tXER"
	d1, cx = bits.Add64(a1, b1, 0)