Date: Tue, 18 Jul 2000 22:10:15 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Marcel Moolenaar <marcel@FreeBSD.org> Cc: cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/i386/include npx.h Message-ID: <Pine.BSF.4.21.0007182158570.1365-100000@besplex.bde.org> In-Reply-To: <200007180412.VAA13490@freefall.freebsd.org>
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On Mon, 17 Jul 2000, Marcel Moolenaar wrote:
> marcel 2000/07/17 21:12:19 PDT
>
> Modified files: (Branch: RELENG_3)
> sys/i386/include npx.h
> Log:
> MFC: change default FPU control word.
>
> PR: 17984
>
> Revision Changes Path
> 1.14.2.2 +5 -35 src/sys/i386/include/npx.h
Um, this change was intentionally left out of RELENG_3. The bug is in the
Linux emulator not keeping up with Linux.
The description misdiagnoses the reason for the exception. I think I
explained this already, but the explanation is not attached to the PR.
In:
float f = FLT_MAX;
double d;
f = f * 2; /* 3 */
d = f; /* 4 */
line 3 causes undefined behaviour due to overflow. RELENG_3 on i386's
was configured so that the undefined behaviour causes a trap on the
FP instruction following the one that overflowed. This instruction
is in line 4, and doesn't exist if line 4 is omitted.
Bruce
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