[U-Boot] [PATCH 2/2] musb: sunxi: Implement dfu_usb_get_reset()

[Ian Campbell]

On Sun, 2015-10-25 at 22:16 +0100, Albert ARIBAUD wrote:
> Hello Ian,
> 
> On Sun, 25 Oct 2015 19:22:00 +0000, Ian Campbell
> <ijc+uboot at hellion.org.uk> wrote:
> > On Sun, 2015-10-25 at 14:22 +0100, Albert ARIBAUD wrote:
> > > On Sun, 25 Oct 2015 12:40:45 +0000, Ian Campbell
> > > > Doesn't the bool return type already cause that to happen?
> (from the
> > > > PoV of the caller at least)
> > > 
> > > When all is said and done, a C bool is a C int,
> > 
> > Not if it is a _Bool (via stdbool.h or some other way).
> > 
> > A _Bool is always either 0 or 1, and scalar value which is
> converted to
> > a _Bool is converted to either 0 or 1.
> >
> > > So no, types, bool or otherwise, do not cause any implicit '!!'
> to
> > > happen.
> > 
> > I believe this is not correct when _Bool is used.
> > 
> > In u-boot a bool is indeed a _Bool (or at least I don't see any
> other
> > typedef's and I can see various includes on stdbool.h, I therefore
> > didn't feel the need to check how bool is arrived at in this
> particular
> > file).
> 
> What you write is possibly correct for C++, but certainly not for C,
> for which booleans are integers, with no compiler-enforced constraint
> on their value domains.

I know next to nothing about C++ so I am certainly not confusing things
with that.

The _Bool type in C99 is an integer which may take on exactly the
values 0 or 1. Since the code which started this subthread was using
"bool" from <stdbool.h> it is _Bool which is being discussed here.

The actual standard costs money (and is therefore unlinkable) but 
http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf is a late
draft and I believe this aspect is unchanged. Section 6.3.1.2 is one
relevant part explaining that a _Bool must always be either 0 or 1:

    When any scalar value is converted to _Bool, the result is 0 if the
    value compares equal to 0; otherwise, the result is 1.

Many of the other clauses dealing with Integers (e.g. 6.3.1.3.1) have
had "other than _Bool" or some similar wording added to them since
_Bool does indeed behave a little differently.

So I'm afraid I disagree with your statement, at least for C >= C99 (I
can't recall if _Bool was in C89, but I think the answer is no).

Ian.