From mboxrd@z Thu Jan  1 00:00:00 1970
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
In-reply-to: Your message of "Fri, 23 Apr 2010 19:53:24 BST."
	<239c41a785c8c5638338c2f007f50733@vitanuova.com>
References: <239c41a785c8c5638338c2f007f50733@vitanuova.com>
From: Bakul Shah <bakul+plan9@bitblocks.com>
Date: Fri, 23 Apr 2010 13:08:14 -0700
Message-Id: <20100423200815.03B385B4A@mail.bitblocks.com>
Subject: Re: [9fans] BUG!!! in Plan9 compiler!
Topicbox-Message-UUID: 0cd3155e-ead6-11e9-9d60-3106f5b1d025

On Fri, 23 Apr 2010 19:53:24 BST C H Forsyth <forsyth@vitanuova.com>  wrote:
> >As per C89 in this case the unsigned char value should be
> >promoted to a *signed* int value.  The sum will be of type
> >signed int and so the division will do the right thing. In
> >kencc case it seems the sum has type unsigned int for some
> >reason and further, the signed divisor (2) is promoted to an
> >unsigned int. Seems like a bug.
>
> on 19 April, I wrote:
> >notably the compiler doesn't implement the value-preserving rules for compar
> isons. ...
> >instead the compiler implements the older unsigned-preserving rule

Does the following assertion fail under plan9?

    int x = 1234, y = -4321;
    unsigned char z = 12;
    int r1, r2;

    r1 = (x + y + z)/2;

    x += z;
    r2 = (x + y)/2;

    assert(r1 == r2);

If so, I consider it a bug; particularly as there is no
overflow involved anywhere.