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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 at redhat dot com>
- Cc: <libc-alpha at sourceware dot org>
- Date: Fri, 19 Apr 2013 19:37:58 +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>
On Fri, 19 Apr 2013, Siddhesh Poyarekar wrote:
> Hi,
>
> I've been trying to reproduce the computation that resulted in the
> conclusion that the __mul implementation in mpa.c has a maximum error
> bound of 1.001ULP. I haven't succeeded in doing that and the best
> estimate I have for maximum error bound is in the range of R^-1ULP,
> i.e. 2^-24ULP. I'm sure I must be doing something wrong, but I can't
> figure out what it is:
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.
--
Joseph S. Myers
joseph@codesourcery.com