Re: Fixing geometic calculation

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От Tom Lane
Тема Re: Fixing geometic calculation
Дата
Msg-id 24956.1249668806@sss.pgh.pa.us
обсуждение исходный текст
Ответ на Re: Fixing geometic calculation  (Sam Mason <sam@samason.me.uk>)
Ответы Re: Fixing geometic calculation  (Sam Mason <sam@samason.me.uk>)
Re: Fixing geometic calculation  (Greg Stark <gsstark@mit.edu>)
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Sam Mason <sam@samason.me.uk> writes:
> On Fri, Aug 07, 2009 at 12:50:39PM -0400, Tom Lane wrote:
>> No, I'm worried about code that supposes that it can divide by (x - y)
>> after testing that FPeq(x,y) is not true.  point_sl() for instance.

> OK, but I'm still not sure what you're getting at.

Underflow.  x!=y does not imply (x-y) != 0, if x and y are sufficiently
small and close together.  The difference could underflow to zero.
        regards, tom lane

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