Re: [RFC][PATCH] A generic boolean

From: Jeff Garzik
Date: Wed Jul 19 2006 - 17:04:08 EST

ricknu-0@xxxxxxxxxxxxxx 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

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;
+#warning You compiler doesn't seem to support boolean types, will set 'bool' as
an 'unsigned char'
+typedef unsigned char bool;
+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)
+enum { false = 0, true = 1 } __attribute__((packed));

How is 'packed' attribute useful here?


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