Re: Inaccurate results from numeric ln(), log(), exp() and pow()

On Thu, Dec 10, 2015 at 2:47 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> This patch, or something nearby, seems to have changed the number of
>> significant figures produced by log() and maybe some of the other
>> functions this patch touched.
>
> Yeah, not surprising.
>
>> It's certainly not obvious from the commit message that this change
>> was expected.
>
> That's on me as author of the commit message, I guess. The rscale
> in most of these functions is exactly the number of fraction digits
> that will be emitted, and we changed the rules for computing it.
> Not by much, in most cases. I don't think we should be too worried
> about being bug-compatible with the old behavior.

It seems to be a loss of 4 digits in every case I've seen.

--
Robert Haas
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