linux-hardening - RE: [PATCH 02/10] compiler.h: add is_const() as a replacement of __is

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Message-ID: <e806dd51b1ac4e289131297fbf30fc37@AcuMS.aculab.com>
Date: Fri, 6 Dec 2024 20:23:59 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Linus Torvalds' <torvalds@...ux-foundation.org>
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Subject: RE: [PATCH 02/10] compiler.h: add is_const() as a replacement of
 __is_constexpr()

...
> > > #define const_NULL(x) _Generic(0 ? (x) : (char *)0, char *: 1, void *: 0)
> > > #define const_true(x) const_NULL((x) ? NULL : (void *)1L))
> > > #define const_expr(x) const_NULL((x) ? NULL : NULL))
> > > I send this morning.
> > > Needs 's/char/struct kjkjkjkjui/' applied.
> >
> > Oh Christ. You really are taking this whole ugly to another level.
> 
> I sort of liked that version in a perverse sort of way.
> It does give you a simple test for NULL (unless you've used 'struct kjkjkjkjui').

Except const_NULL() really doesn't work at all - so you are lucky :-)

So maybe the slightly long lines:
#define const_true(x) _Generic(0 ? (void *)((x) + 0 ? 0L : 1L) : (char *)0, char *: 1, void *: 0)
#define const_expr(x) _Generic(0 ? (void *)((x) + 0 ? 0L : 0L) : (char *)0, char *: 1, void *: 0)

I make that 98 characters.
Of course, you can remove all the spaces, only one of the constants need the L suffix
and 'int' is a shorter type name.
That cuts is down to 76:
#define const_expr(x) _Generic(0?(void*)((x)+0?0L:0):(int*)0,int*:1,void*:0)
which starts looking like the TECO commands to parse its command line!

	David

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