Re: [boost] [xint] Third release is ready, requesting preliminary review

Subject: Re: [boost] [xint] Third release is ready, requesting preliminary review
From: Chad Nelson (chad.thecomfychair_at_[hidden])
Date: 2010-05-03 13:22:38

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On 05/03/2010 12:42 PM, vicente.botet wrote:

> I have some question about the interface.
> 
> I know that these functions appears on N1744
> bool getbit( intege r const &, size _t );
> void setbit( intege r &, size_t );
> void clearbit( integer &, size_ t );
> 
> But are these really necessary? A use case?

setbit can be used to create a large power-of-two more efficiently than
a shift function -- that's what the pow2 convenience function uses. I
haven't found a use for the other two, but I imagine that the use case
for them was using a large integer as an unlimited-length bit field.

> The std::numeric_limits specialization defines functions that return 0 with a comment 
> 
> 00298 namespace std {
> 00299 template<>
> 00300 class numeric_limits<boost::xint::integer> {
> 00301     public:
> 00302     static const bool is_specialized = true;
> 00303 
> 00304     static boost::xint::integer min() throw() { return 0; } // Not applicable
> 00305     static boost::xint::integer max() throw() { return 0; } // Not applicable
> 
> If a value can not be given, shouldn't these be undefined?

If they weren't defined, could generic code work with them? The GCC
specialization for the int type includes all of the members, even the
ones that are only applicable to floating-point values, so I did too.

> Or should these functions return -infinity, infinity?

If I had such values, I'd use them there.

> xint::integer is a signed integer. It is worth having an unsigned
> integer xint::uinteger? If not why?

I'd say the question is why have one, rather than why not. :-)

There are only two advantages I know of to unsigned int over int: you
never have to check whether it's negative, and you get one extra bit's
worth of room, allowing you to work with larger numbers. The second
isn't a problem here, and the first can easily be dealt with. Is there a
use case where a signed integer wouldn't be sufficient?
- -- 
Chad Nelson
Oak Circle Software, Inc.
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