NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part1/3346

Internet Message Format | 1996-08-05 | 1.8 KB

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From: Lawrence Kirby <[e-mail]>
Newsgroups: comp.lang.c
Subject: Re: quick decision: is n a power of 2?
Date: Sun, 28 Jan 96 01:12:22 GMT
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In article <[e-mail]>
           [e-mail] "Dan Pop" writes:

>The unary minus operator applied to an unsigned integer is always evaluated
>using two's complement arithmetic, no matter what representation is used
>by the implementation for signed integers.

Not exactly. Two's complement is a representation for signed integers so
unsigned arithmetic clearly doesn't use it. However the nice thing about
2's complement arithmetic is that in most instances the underlying bit
manipulations are (or can be for a suitable definition of overflow behaviour)
the same as those for unsigned arithmetic (so at the archetecture
level a single form of, e.g. an ADD instruction, can deal with both).

So the expression (-5) and (-5U) are each evaluated by its own set of rules
but where signed integers are represented in 2's complement the 2 results
will have the same underlying bit pattern.

>Tanmoy's point was that by restricting the solution to unsigned integers,
>the representation of signed integers becomes irrelevant.

That's my point too! :-)

--
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Lawrence Kirby | [e-mail]
Wilts, England | [e-mail]
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