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From: "Al Grant" <AlGrant@myrealbox.com> To: nobody@gcc.gnu.org Cc: gcc-prs@gcc.gnu.org, Subject: Re: c/7284: incorrectly simplifies leftshift followed by signed power-of-2 division Date: Fri, 12 Jul 2002 08:06:00 -0000 [thread overview] Message-ID: <20020712150601.21796.qmail@sources.redhat.com> (raw) The following reply was made to PR c/7284; it has been noted by GNATS. From: "Al Grant" <AlGrant@myrealbox.com> To: nathan@gcc.gnu.org, algrant@acm.org, gcc-bugs@gcc.gnu.org, gcc-prs@gcc.gnu.org, nobody@gcc.gnu.org, gcc-gnats@gcc.gnu.org Cc: Subject: Re: c/7284: incorrectly simplifies leftshift followed by signed power-of-2 division Date: Fri, 12 Jul 2002 15:00:34 +0000 On 12/07/2002 15:12:01 nathan wrote: >Synopsis: incorrectly simplifies leftshift followed by signed power-of-2 >division > >State-Changed-From-To: open->closed >State-Changed-By: nathan >State-Changed-When: Fri Jul 12 07:12:01 2002 >State-Changed-Why: >not a bug. for signed types, if 'n << c' overflows, the >behaviour is undefined. There is no "overflow" in my sample code. The operation of shifting 128 24= bits to the left on a 32-bit machine produces the bit pattern 0x80000000. No bits overflow. The fact that a positive number may become negative when left-shifted is a = property of the twos complement representation. The standard does not de= fine signed left shift in terms of multiplication and certainly doesn't s= ay that it is undefined when the apparently equivalent multiplication wou= ld be undefined.
next reply other threads:[~2002-07-12 15:06 UTC|newest] Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top 2002-07-12 8:06 Al Grant [this message] -- strict thread matches above, loose matches on Subject: below -- 2003-02-13 16:06 rearnsha 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 7:12 nathan 2002-07-12 4:26 algrant
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