RE: [avr-gcc-list] C coding question

[Eric Weddington]

> -----Original Message-----
> From: 
> address@hidden 
> [mailto:address@hidden
> org] On Behalf Of Paulo Marques
> Sent: Monday, October 09, 2006 4:39 AM
> To: larry barello
> Cc: address@hidden
> Subject: Re: [avr-gcc-list] C coding question
> 
> larry barello wrote:
> > [...]
> > So I said:
> > 
> > (bSomeBool?1:0) ^ ((SomeBitMask & SomeVariable)?1:0))
> 
> Since no one else made this comment, I just wanted to point 
> out that you 
> can write that as:
> 
> (bSomeBool ^ (!!(SomeBitMask & SomeVariable)))
> 
> "!!" is often used to convert an integer value into a logical (0/1) 
> value. Maybe it is easier to the compiler than "?1:0".

I would question the "often used" phrase; this is the first I've heard of it
in 15 years of programming in C.

If you want a logical (boolean) XOR operation, you can write the expression
simply:

#include <stdbool.h>
...
(bool)(bSomeBool != (bool)(SomeBitMask & SomeVariable))

Remember that the type of an equality/non-equality operator is another
boolean value. Be sure to typecast the bitwise and operation to a bool value
so the != operator is comparing values of the same type.