Re: [boost] [xint] Design Question

Subject: Re: [boost] [xint] Design Question
From: Chad Nelson (chad.thecomfychair_at_[hidden])
Date: 2010-06-17 12:04:05

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On 06/17/2010 07:10 AM, Stewart, Robert wrote:

>>> What about making the difference between two unsigned integers a 
>>> signed integer?
>> 
>> That sounds like a useful behavior, but if the developer using the 
>> library says it should be an unsigned number, I don't think the
>> library should override that.
> 
> According to an old C book I have (C: A Reference Manual, 2nd ed,
> Harbison and Steele), "the result of subtracting one unsigned integer
> from another is always unsigned and therefore cannot be negative."

Yes, that's the way I've always understood it. I've often taken
advantage of that too -- typecasting -1 to an unsigned type gives a
value with all bits on, and doesn't require you to know how many bits
that type has beforehand. (Yes, there are other ways to do it, like with
operator~.)

> That may not be definitive, and the C++ standard doesn't dictate the
> type of the result other than, perhaps, by incorporating the C
> standard to which I have no access, but it certainly sets
> expectations that your library ought not violate.

Pretty much what I was thinking.
- -- 
Chad Nelson
Oak Circle Software, Inc.
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