Date: Sun, 31 Jan 2010 02:20:30 +1100 (EST) From: Bruce Evans <brde@optusnet.com.au> To: gavin@freebsd.org Cc: das@freebsd.org, freebsd-standards@freebsd.org, freebsd-amd64@freebsd.org Subject: Re: standards/143358: nearbyint raises spurious inexact exception Message-ID: <20100131014341.J78095@delplex.bde.org> In-Reply-To: <201001301251.o0UCpSEP077706@freefall.freebsd.org> References: <201001301251.o0UCpSEP077706@freefall.freebsd.org>
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On Sat, 30 Jan 2010 gavin@freebsd.org wrote: > Synopsis: nearbyint raises spurious inexact exception > Note that a comment in the function itself in lib/msun/src/s_nearbyint.c > does also suggest that this PR is valid, "We save and restore the > floating-point environment to avoid raising an inexact exception." I've > also verified Solaris 10, Linux and FreeBSD 7.2 show the expected behaviour. This seems to be a bug in gcc-4.2, or perhaps a bug in the inline asms. gcc-4.2 still works with -O0, but with -O it removes the entire fesetenv() in nearbyint(). The fegetenv() isn't removed though its result is never used. I didn't get anywhere good trying to fix this, but I got to the following worse place of interest: after replacing the fesetenv(&env) by fesetenv(&xenv) where xenv is an invalidly initialized global variable (all 0's), the fegetenv(&env) corrupted the current environment (looks a bit like xenv was used to initialize the current environment). Removing fesetenv() in other contexts would give larger bugs. Bruce
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