On 8/20/2016 3:16 PM, Martin Buchholz wrote:
On Sat, Aug 20, 2016 at 12:32 PM, Martin Buchholz <marti...@google.com <mailto:marti...@google.com>> wrote:Quibble: "guaranteed" may be true in practice, but longBitsToDouble is technically permitted to reset the sign bit back to 1 if the hardware is hostile. Because of this, I would simply remove the word "guaranteed".After reading IEEE 754 2008 6.2.1. , I now believe signalling NaNs have to use the significand bits; the sign bit is free to use; and so I retract my quibble, and am happy with the word "guaranteed".
Right; the sign bit of a NaN has very little meaning. The hardware guys like to be able to do things like for a floating-point multiply "sign bit of output = XOR of sign bits of inputs" without having to do inconvenient NaN checks :-) The NaN payload for retrospective diagnostics is all in the significand.
Cheers, -Joe
