c1, r1lo := shiftRightBy51(&r1)
	c2, r2lo := shiftRightBy51(&r2)
	c3, r3lo := shiftRightBy51(&r3)
	c4, r4lo := shiftRightBy51(&r4)
	maskAndAdd(r0lo, maskLow51Bits, c4, 19)
	maskAndAdd(r1lo, maskLow51Bits, c0, 1)
	maskAndAdd(r2lo, maskLow51Bits, c1, 1)
	maskAndAdd(r3lo, maskLow51Bits, c2, 1)
	maskAndAdd(r4lo, maskLow51Bits, c3, 1)

	Comment("Second reduction chain (carryPropagate)")
	// c0 = r0 >> 51
	MOVQ(r0lo, c0)
	SHRQ(Imm(51), c0)