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Re: Is the maximum error bound in __mul really 1.001ULP?
- From: "Joseph S. Myers" <joseph at codesourcery dot com>
- To: Siddhesh Poyarekar <siddhesh dot poyarekar at gmail dot com>
- Cc: Siddhesh Poyarekar <siddhesh at redhat dot com>, GNU C Library <libc-alpha at sourceware dot org>
- Date: Sun, 21 Apr 2013 15:07:05 +0000
- Subject: Re: Is the maximum error bound in __mul really 1.001ULP?
- References: <20130419111759 dot GA10160 at spoyarek dot pnq dot redhat dot com> <Pine dot LNX dot 4 dot 64 dot 1304191936110 dot 27838 at digraph dot polyomino dot org dot uk> <CAAHN_R1qAy1ysFhpFoA-QrvQoo7jxzeDKdc9FwqvC2aa8Ksp+g at mail dot gmail dot com>
On Sat, 20 Apr 2013, Siddhesh Poyarekar wrote:
> > A conclusion that the error bound is less than 0.5ulp (that is, ulps of a
> > value with the precision to which the result gets rounded) is implausible.
> > If you get such a conclusion I suppose you must be counting ulps in some
> > way different from the statement that the bound is 1.001ulp.
>
> Agreed, which is why I posted my derivation too. Do you think there's
> something wrong with it?
I didn't see any point in analysis of the derivation when the conclusion
clearly doesn't make sense.
--
Joseph S. Myers
joseph@codesourcery.com