RE: [PATCH 00/13] [RFC] Rust support

[David Laight]

From: Peter Zijlstra
> Sent: 17 April 2021 12:17
...
> > (i'd argue this is C being broken; promoting only as far as int, when
> > assigning to an unsigned long is Bad, but until/unless either GCC fixes
> > that or the language committee realises that being stuck in the 1970s
> > is Bad, people are going to keep making this kind of mistake)
> 
> Well, I think the rules actually make sense, at the point in the syntax
> tree where + happens, we have 'unsigned char' and 'int', so at that
> point we promote to 'int'. Subsequently 'int' gets shifted and bad
> things happen.

The 1970s were fine.
K&R C was sign preserving - so 'unsigned char' promoted to 'unsigned int'.
The ANSI C committee broke things by changing it to value preserving
with the strong preference for signed types.

Even with ANSI C the type of ((unsigned char)x + 1) can be unsigned!
All it needs as an architecture where sizeof (int) == 1.
(sizeof (char) has to be 1 - even though that isn't directly explicit.)

Of course, having 32-bit 'char' and 'int' does give problems with
the value for EOF.

	David

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