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Re: Is the maximum error bound in __mul really 1.001ULP?


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


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