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

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com>
Cc: PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Inaccurate results from numeric ln(), log(), exp() and pow()
Date: 2015-11-14 00:42:49
Message-ID: 12881.1447461769@sss.pgh.pa.us
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Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com> writes:
> On 14 November 2015 at 00:16, Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com> wrote:
>> I can't see a way to make that work reliably. It would need to be
>> 10^estimate_ln_weight(base) and the problem is that both exp and
>> ln_weight could be too big to fit in double variables, and become
>> HUGE_VAL, losing all precision.

> Of course I meant 10^ln_weight could be too big to fit in a double.

Drat, that's the second time in this review that I've confused
ln_weight(x) with ln(x). Time to call it a day ...

regards, tom lane

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