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SubjectRe: [BUG] Bad #define, nonportable C, missing {}

On 20011122 Stevie O wrote:
>At 12:35 PM 11/21/2001 +0000, Vincent Sweeney wrote:
>> > Bad code style. Bad name (sounds like 'module inc').
>> > I can't even tell from this define what the hell it is trying to do:
>> > x++ will return unchanged x, then we obtain (x mod y),
>> > then we store it into x... and why x++ then??!
>> > Alan, seems like you can help here...
>>Go read up on C operator precedence. Unary ++ comes before %, so if we
>>rewrite the #define to make it more "readable" it would be #define
>>MODINC(x,y) (x = (x+1) % y)
>But x++ is postincrement though. That means the value of 'x' is inserted,
>and after the expression is evaluated, x is incremented. Right?
>If we were going to be semiobscure, wouldn't the correct code be
>#define MODINC(x,y) (x = ++x % y)

But the question is: Is this kind of code worth the discussion ? AFAIK,
gcc is enough smart to change *2 to <<1, so wouldn't it be smart to
detect a +1 and use and inc (and perhaps to detect that x is overwritten so it
can do the op in place).
So write it as
x = (x+1)%y
and make it readable.

J.A. Magallon # Let the source be with you...
Mandrake Linux release 8.2 (Cooker) for i586
Linux werewolf 2.4.15-pre9 #1 SMP Thu Nov 22 16:16:54 CET 2001 i686
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