52 bits of payload, and at least one bit must be set.

You can put stuff into the sign bit too, that makes 53. Yeah, the lower 52 bits can't all be zero - that'd be ±INF, but the other 2^53-2 values are all yours to use.

	▲	pklausler 2 days ago \| parent [-]
		It's possible for the sign bit of a NaN to be changed by a "non-arithmetic" operation that doesn't trap on the NaN, so don't put anything precious in there.