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From: rearnsha@gcc.gnu.org
To: algrant@acm.org, gcc-bugs@gcc.gnu.org, gcc-prs@gcc.gnu.org,
	nobody@gcc.gnu.org
Subject: Re: c/7284: incorrectly simplifies leftshift followed by signed power-of-2 division
Date: Thu, 13 Feb 2003 16:06:00 -0000	[thread overview]
Message-ID: <20030213160623.16022.qmail@sources.redhat.com> (raw)

Synopsis: incorrectly simplifies leftshift followed by signed power-of-2 division

State-Changed-From-To: closed->open
State-Changed-By: rearnsha
State-Changed-When: Thu Feb 13 16:06:23 2003
State-Changed-Why:
    I'm re-opening this report.  In c89 the text for << says
    
    The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are filled with zeros.
    
    It then goes on to qualify what this means when E1 is unsigned, but says nothing about the *interpretation* for the signed context (beyond what is specified above).  However, in a 2s complement environment it is possible to give a meaningful interpretation of the resulting value.
    
    DR#081 says that the meaning in the signed context is "implementation defined", but that is clearly very different from "undefined" as we have at present.
    
    At the very least we must document what left shift of a signed value means on our implementation.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=7284


             reply	other threads:[~2003-02-13 16:06 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-02-13 16:06 rearnsha [this message]
  -- strict thread matches above, loose matches on Subject: below --
2002-07-12 12:56 Nathan Sidwell
2002-07-12 10:06 Falk Hueffner
2002-07-12  9:46 Nathan Sidwell
2002-07-12  9:26 Falk Hueffner
2002-07-12  8:16 Falk Hueffner
2002-07-12  8:06 Al Grant
2002-07-12  7:12 nathan
2002-07-12  4:26 algrant

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