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Re: Fix x86/x86_64 expm1l spurious underflow exceptions (bug 16539)
- From: Andreas Jaeger <aj at suse dot com>
- To: "Joseph S. Myers" <joseph at codesourcery dot com>, libc-alpha at sourceware dot org
- Date: Tue, 24 Jun 2014 22:50:46 +0200
- Subject: Re: Fix x86/x86_64 expm1l spurious underflow exceptions (bug 16539)
- Authentication-results: sourceware.org; auth=none
- References: <Pine dot LNX dot 4 dot 64 dot 1406242046500 dot 21652 at digraph dot polyomino dot org dot uk>
On 06/24/2014 10:47 PM, Joseph S. Myers wrote:
> This patch fixes bug 16539, spurious underflow exceptions from x86 /
> x86-64 expm1l. The problem is that the computation of a base-2
> exponent with extra precision involves spurious underflows for
> arguments that are small but not subnormal, so a check is added to
> just return the argument in those cases. (If the argument *is*
> subnormal, underflowing is correct and the existing code will always
> underflow, so it suffices to keep using the existing code in that
> case; some expm1 implementations have a bug (bug 16353) with missing
> underflow exceptions, but I don't think there's such a bug in this
> particular version.)
Thanks,
Andreas
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