Re: [boost] [xint] Design Question

Subject: Re: [boost] [xint] Design Question
From: Scott McMurray (me22.ca+boost_at_[hidden])
Date: 2010-06-16 21:32:39

On 16 June 2010 06:57, Chad Nelson <chad.thecomfychair_at_[hidden]> wrote:
>
> C: Throw an exception if any calculation results in a negative number.
> (Not very useful, but logical because under the built-in types' unsigned
> rules, a negative number in an unlimited-length library would be
> infinitely long.)
>

That results in look-before-you leap, which is probably bad for speed
here, since the subtraction is similar in cost to the comparison.

Though it does feel like the best option for operator--(), since there
the look is cheap.

>
> D: Force any negative numbers to a different value, such as zero or
> maybe their positive counterparts. (I can't think of any use for this, I
> just put it here for completeness.)
>

Force to zero is "saturation", which is a legitimate desire in certain
situations, so it might not be as useless as you think.

Making subtraction be absolute difference in an interesting option,
since it at least keeps the a-b = 0 <=> a = b equivalence intact.

>
> Can anyone think of a potential reason for options C or D? Or a reason
> to prefer option B? Or maybe come up with a different idea entirely?
>

How about this combo of B, C, and D:
- if !i, --i and i-- both throw exceptions.
- a - b doesn't compile for non-fixed length
- provide a separate absdiff(a, b) function

~ Scott