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Re: Patch for locale/programs/3level.h
- To: haible at ilog dot fr
- Subject: Re: Patch for locale/programs/3level.h
- From: Paul Eggert <eggert at twinsun dot com>
- Date: Tue, 7 Aug 2001 00:31:51 -0700 (PDT)
- CC: libc-alpha at sources dot redhat dot com, aj at suse dot de
- References: <firstname.lastname@example.org>
> From: Bruno Haible <email@example.com>
> Date: Mon, 6 Aug 2001 22:25:39 +0200 (CEST)
> > We noticed a problem with ~0 nesting in 3level.h. The following looks
> > more sane to me.
> > - if (lookup1 != ~((uint32_t) 0))
> > + if (lookup1 != (uint32_t) ~0)
> The values are not the same....
> The first value is definitely the intended one.
It's true that they're not the same, but surely the second value is
what is intended here.
Assuming a twos-complement platform, (~0) evaluates to -1, and hence
((uint32_t) ~0) evaluates to 0xFFFFFFFF regardless of int width.
Conversly, ~((uint32_t) 0) does not always evaluate to 0xFFFFFFF. For
example, if int is 64 bits, it evaluates to -1, which is
0xFFFFFFFFFFFFFFFF (again, assuming twos-complement).
Here's a better patch:
- if (lookup1 != ~((uint32_t) 0))
+ if (lookup1 != (uint32_t) -1)
(uint32_t) -1 is the usual way to write an all-one's pattern.
It has the somewhat-theoretical advantage of being portable to
ones-complement and to signed-magnitude hosts, whereas (uint32_t) ~0
is not portable to such hosts. It has the more important advantage of
being the usual way to write an all-ones unsigned value, which means
it's easier for other people to understand the code.