Re: [boost] [serialisation] reading and writing reals

From: John Maddock (john_at_[hidden])
Date: 2006-03-17 14:32:03

> A very brief look at this suggests that starting with values < 0.001
> that cause trouble.
> So random testing may have trouble finding this.

Confirmed, there appear to be other problems with random tests that I'll 
address in a separate message.

> Using nextafter always seems to produce 35% or 3 % of values wrong
> (by one bit).
>
> Starting with 0.0001

Also confirmed, and the problem areas appear to be different for floats and 
doubles which makes them rather hard to find, and any kind of systematic 
testing of std lib's next to impossible.

> But I am concerned that we have a really good test for it, or that it
> is provably correct, or better still both ;-))
>
> With float, one can just about do a full test - takes all night.
>
> But even with my new Dual Core AMD X2 ;-))
>
> an exhaustive double won't finish before it is worn out :-((

Quite.

Proving the code correct is tricky though, when I've more time I'll double 
check with Knuth Vol 2 and with ACM and see if there's any literature that 
can help out.

John.