Preliminary submission - std.rational and std.typelist

[Simen Kjaeraas]

On 2012-44-08 06:10, Arlen <arlen.ng at gmx.com> wrote:

> On Sat, Oct 6, 2012 at 1:32 PM, Dmitry Olshansky <dmitry.olsh at gmail.com>  
> wrote:
>>
>> Cool, does it work with BigInt?
>>
>
> No it doesn't work with BigInt, but I did look into it today briefly.
> There are issues with BigInt that I'm not sure what to do about:
>
> 1.  To convert a BigInt to floating-point one needs to convert it to
> the built-in integer types first.  If you go beyond the limits of the
> built-in types (long), then what's the point?  You might as well be
> using int or long.

I thought (part of) the point of Rational was to use it when it would
be more fitting than floating-point. If it's only there to be converted
to floating-point, I don't know what it's there for.

As for a workaround, right-shift num and den to reasonable values
(which fit in a long), divide to get a float, and multiply by
2.0^^(log2(num)-log2(den)). Oughta work.


> 2.  The functions in std.math don't support BigInt, and most likely
> never will.  Even if they did, you would still need multi-precision
> floating point to store the irrational numbers.  If you decided to use
> the built-in types, then again what's the point?  You might as well go
> with int or long.

The only function you use from std.math is abs, right? That should be
fairly easy to implement for BigInt.

It'd mean you'd have to specialize a bit for BigInt, though (just
create your own abs function that calls the correct one).

Another option: lobby for BigInt support in std.math. :p


Also, irrational numbers? How'd you get those in a *Rational* library? :p


-- 
Simen