linux-kernel - Re: [PATCH] arm: nomadik: avoid assigning u32 to bool

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Date:	Sun, 3 Apr 2011 12:52:46 +0200
From:	Alessandro Rubini <rubini@...pv.it>
To:	nikai@...ai.net
Cc:	rabin@....in, linus.walleij@...ricsson.com,
	STEricsson_nomadik_linux@...t.st.com, linux@....linux.org.uk,
	tglx@...utronix.de, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm: nomadik: avoid assigning u32 to bool

>> Why?  There are dozens of places in the kernel where this done, the code
>> generated should be the same, and it's pretty obvious what is being done
>> as it is.
> 
> Primarily because we were asked to avoid casts to bool even if
> they are safe.

[I have studied, meanwhile]

Actually the point of Rabin is, I think, that the patch is not needed.
Our "bool" is the C99 "_Bool" type, for which the compiler
automatically converts all non-0 assignments to 1.  Even if storage
is still one byte.

IIUC, the point of _Bool is allowing comparisong with "true", while in
general non-0 is considered true if evaluated in a conditional
but may be "!= 1" so "!= true" if compared explicitly.

You can compile a one-liner to check. I used a few more:

    _Bool i[10];

    int main(void)
    {
        i[0] = 1;
        i[1] = 10;
        return i[0];
    }

/alessandro
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