Re: [RFC][PATCH] fix abs() macro to work with types wider than int

[linux-os \(Dick Johnson\)]

On Wed, 25 Apr 2007, Andreas Schwab wrote:

> "linux-os (Dick Johnson)" <linux-os@xxxxxxxxxxxx> writes:
>
>> I think this works, regardless of the length of the integers:
>>
>> #define abs(x) (((x)<0)?-(x):(x))
>
> But it evaluates its argument more than once.
>
> Andreas.
>

Sure. Macros do that. If that's not okay, then you need either
a temporary variable or a function. The original query was for
a macro. Any macro that tests something then returns a value
based upon the test is going to have that problem. Any attempt
to just AND off a sign bit is going to have width problems. You
can't have your cake and eat it too. Even whacking off the sign-
bit may fail because there may be two variable accesses which could
mean two function calls, destroying the logic.


Cheers,
Dick Johnson
Penguin : Linux version 2.6.16.24 on an i686 machine (5592.62 BogoMips).
New book: http://www.AbominableFirebug.com/
_


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