On Sat, Sep 12, 2020 at 05:37:23PM -0700, Christopher Barker wrote:
> On Sat, Sep 12, 2020 at 5:05 PM Steven D'Aprano <[email protected]> wrote:
> > IEEE-754 requires that float literals overflow to infinity.
>
> sure, which means that, e.g. 1e100 * 1e300 would overflow to Inf.
>
> But that doesn't say anything about interpreting a literal. I don't if C
> libs necessarily parse:
Sorry, I didn't explain correctly. What I attempted, but failed, to say
is that the standard requires that if the float literal cannot be
represented as a numeric value because it would overflow, then it should
be interpreted as an infinity.
So `1e300` can be represented as a double precision float, so that's
what you get, but `1e1000` cannot be, it overflows, so you get infinity
instead.
This doesn't mean that the standard requires the parser to read the
mantissa and exponent separately and actually perform a multiplication
and power.
I expect that the standard will require *correctly rounded* results. So
for example, this literal rounds down to the largest possible finite
float:
py> 1.7976931348623158e+308
1.7976931348623157e+308
but this literal rounds up to infinity:
py> 1.7976931348623159e+308
inf
because the closest representable binary number to 1.79...159e+308 would
overflow the available bits.
> So that's what I'm wondering -- is there a standard that says the a
> too-large literal should overflow, and therefgor create and inf, rather
> than being an error.
Yep, that's what I'm saying :-)
Or at least tried to say.
--
Steve
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