linux-kernel - Re: [RFC][PATCH] A generic boolean

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Message-ID: <20060719212049.GA6828@martell.zuzino.mipt.ru>
Date:	Thu, 20 Jul 2006 01:20:49 +0400
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	ricknu-0@...dent.ltu.se
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] A generic boolean

On Wed, Jul 19, 2006 at 10:38:20PM +0200, ricknu-0@...dent.ltu.se wrote:
> A first step to a generic boolean-type. The patch just introduce the bool (in
> arch. i386 only (for the moment)),

What's do special about i386?

> false and true + fixing some duplications in
> the code.

> -Why would we want it?
> -There is already some how are depending on a "boolean"-type (like NTFS). Also,
> it will clearify functions who returns a boolean from one returning a value, ex:
> bool it_is_ok();
> char it_is_ok();
> The first one is obvious what it is doing, the secound might return some sort of
> status.

It should be obvious from name whether function returns int which is a
boolean or int which is a number.

> -Why false and not FALSE, why not "enum {...} bool"
> -They are not #define(d) and shouldn't because it is a value, like 'a'. But
> because it is just a value, then bool is just a variable and should be able to
> handle 0 and 1 equally well.

  -Why we wouldn't want it
  -C++ and Java fans will treat bool as a green light to the following

	if (!(flags == true))
  and
	if (!(flags == false))

> If this takes off, I guess I will spend quite some time at kernel-janitors
> "cleaning" those who use a boolean-type.

> Yes, I know about Andrew's try to unify TRUE and FALSE, did read the thread with
> interest (that's from where I got to know about _Bool). But mostly (then still
> on the subject) was some people did not want FALSE and TRUE instead of 0 and 1.
> I look at it as: 'a' = 97, if someone like to write 97 instead of 'a', please do
> if you find it easier to read. I, on the other hand, think it is easier with
> 'a', false/FALSE, NULL, etc.
> DS
> 
> PPS
> One thing about _Bool thue:
> _Bool a = 12; results in a = 1
> 
> test( char * t ) { t = 12; }
		    ^^^
> main() {
> _Bool a;
> test( (char *) &a ); results in a = 12.
> }
> 
> But I do not think of it as a problem since a "true" is just !false. Doing:
> if (boolvar == true)
> seems odd, after all...
> 
> ... and sorry for the longwinded letter :)
>

Please, show compiler flag[s] to enable warning[s] from gcc about

	_Bool foo = 42;

Until you do that the whole activity is moot.

> --- a/drivers/net/dgrs.c
> +++ b/drivers/net/dgrs.c
> @@ -110,7 +110,6 @@ static char version[] __initdata =
>   *	DGRS include files
>   */
>  typedef unsigned char uchar;
> -typedef unsigned int bool;
>  #define vol volatile
>  
>  #include "dgrs.h"

The only chunk that looks OK to me.

> --- a/include/asm-i386/types.h
> +++ b/include/asm-i386/types.h
> @@ -10,6 +10,15 @@ typedef unsigned short umode_t;
>   * header files exported to user space
>   */
>
> +#if defined(__GNUC__) && __GNUC__ >= 3
> +typedef _Bool bool;
> +#else
> +#warning You compiler doesn't seem to support boolean types, will set 'bool' as
> an 'unsigned char'
> +typedef unsigned char bool;

Why unsigned char? Why not unsigned int? What would this do wrt
bitfields?

> +#endif
> +
> +typedef bool u2;

What is it?

-
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