Date: Mon, 10 Apr 2000 21:40:04 -0700 (PDT) From: Bruce Evans <bde@zeta.org.au> To: freebsd-bugs@FreeBSD.org Subject: Re: i386/17914: float-to-double core dump on 3.4R Message-ID: <200004110440.VAA48579@freefall.freebsd.org>
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The following reply was made to PR i386/17914; it has been noted by GNATS. From: Bruce Evans <bde@zeta.org.au> To: aa8vb@ipass.net Cc: FreeBSD-gnats-submit@FreeBSD.ORG Subject: Re: i386/17914: float-to-double core dump on 3.4R Date: Tue, 11 Apr 2000 14:39:21 +1000 (EST) On Mon, 10 Apr 2000 aa8vb@ipass.net wrote: > >Description: > > #include <float.h> > > main() > { > float f = FLT_MAX; > double d; > f = f * 2; > d = f; > } > > Delete the "d=f" line and it doesn't core. Put it in and it does > (floating-point exception). > > From this it appears there may be a bug in the float-to-double > promotion when f is Inf (or, at least I'd expect that f is Inf). No. "f * 2" gives undefined behaviour since it overflows. For FreeBSD-3.4 on i386's, the actual behaviour is to leave the operands on the FP stack and cause a SIGFPE on the next FP instruction after the one that overflowed. > Note that the core dump does not occur when the Inf is generated, > but only when it is promoted to a double. Inf is not generated. The operands are left on the FP stack for the SIGFPE handler to fix up. This behaviour is easy to see using gdb ("display/i $pc", "stepi" and "info float"). Bruce To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-bugs" in the body of the message
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