Re: rounding problems

From: Sam Mason <sam(at)samason(dot)me(dot)uk>
To: pgsql-general(at)postgresql(dot)org
Subject: Re: rounding problems
Date: 2008-05-14 14:38:17
Message-ID: 20080514143817.GF1657@frubble.xen.chris-lamb.co.uk
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On Tue, May 13, 2008 at 02:36:18PM -0400, Justin wrote:
> Double holds 15 places which is the highest value of precision it can
> maintain before rounding occurs.
>
> Is is limit less no, but what is?
>
> Practically speaking taking a vale 0.000,000,000,000,001 aka
> 1 trillionth of anything,

But remember that if you add this value onto a large number and then
take off the large number the result will be zero.

(0.000,000,000,01 + 1,000,000) - 1,000,000 ==> 0
0.000,000,000,01 + (1,000,000 - 1,000,000) ==> 0.000,000,000,01

In general, operations on floating point numbers will increase their
errors.

> i view the problem solved for 98% of problems.

Floating point math is good for most problems, hence why most languages
expose the abstraction.

Sam

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