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

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Date:	Wed, 19 Jul 2006 17:04:56 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	ricknu-0@...dent.ltu.se
CC:	linux-kernel@...r.kernel.org, Andrew Morton <akpm@...l.org>
Subject: Re: [RFC][PATCH] A generic boolean

ricknu-0@...dent.ltu.se wrote:
> A first step to a generic boolean-type. The patch just introduce the bool (in

Since gcc supports boolean types and can optimize for such, introducing 
bool is IMO a good thing.


> -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.

A better reason is that there is intrinsic compiler support for booleans.


> -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.
> 
> Well, this is _my_ opinion, it may be totally wrong. If so, please tell me ;)

> 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.

We should follow what C99 directs.


> diff --git a/include/asm-i386/types.h b/include/asm-i386/types.h
> index 4b4b295..e35709a 100644
> --- 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;
> +#endif
> +
> +typedef bool u2;

NAK.  gcc >= 3 is required by now, AFAIK.

Also, you don't want to force 'unsigned char' on code, because often 
code prefers a machine integer to something smaller than a machine integer.


> diff --git a/include/linux/stddef.h b/include/linux/stddef.h
> index b3a2cad..5e5c611 100644
> --- a/include/linux/stddef.h
> +++ b/include/linux/stddef.h
> @@ -10,6 +10,8 @@ #else
>  #define NULL ((void *)0)
>  #endif
>  
> +enum { false = 0, true = 1 } __attribute__((packed));

How is 'packed' attribute useful here?

	Jeff


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