Re: port-hp300/50852: src/sys/arch/hp300/stand/common/ite.c:239: bad expression

[Joerg Sonnenberger <joerg%britannica.bec.de@localhost>]

The following reply was made to PR port-hp300/50852; it has been noted by GNATS.

From: Joerg Sonnenberger <joerg%britannica.bec.de@localhost>
To: David Binderman <dcb314%hotmail.com@localhost>
Cc: "gnats-bugs%NetBSD.org@localhost" <gnats-bugs%netbsd.org@localhost>,
	"port-hp300-maintainer%netbsd.org@localhost" <port-hp300-maintainer%netbsd.org@localhost>,
	"gnats-admin%netbsd.org@localhost" <gnats-admin%netbsd.org@localhost>,
	"netbsd-bugs%netbsd.org@localhost" <netbsd-bugs%netbsd.org@localhost>
Subject: Re: port-hp300/50852: src/sys/arch/hp300/stand/common/ite.c:239: bad
 expression
Date: Fri, 26 Feb 2016 21:24:14 +0100

 On Fri, Feb 26, 2016 at 04:45:21PM +0000, David Binderman wrote:
 > Hello there,
 > 
 > ----------------------------------------
 > > On Fri, Feb 26, 2016 at 10:55:00AM +0000, dcb314%hotmail.com@localhost wrote:
 > >>>Description:
 > >> [src/sys/arch/hp300/stand/common/ite.c:239]: (error) Expression 'whichconsole=++whichconsole%(NITE+1)' depends on order of evaluation of side effects
 > >>
 > >> Source code is
 > >>
 > >> whichconsole = ++whichconsole % (NITE+1);
 > >>
 > >> Maybe better code
 > >>
 > >> whichconsole = (whichconsole + 1) % (NITE+1);
 > >
 > > Independent of the question of which code is better, I don't think the
 > > error is correct. 
 > 
 > False, the error is valid.
 > 
 > There are two writes to whichconsole, one on the left of the assignment,
 > one on the right.
 > 
 > The ISO standard doesn't define which order those writes occur.
 > See Steve Summit's C FAQ for sequence points, section 3.8.
 
 You are wrong. There is no write from the left operand of the
 assignment. The write is the result of the assignment and as written
 before is explicitly sequenced by the standard.
 
 Joerg