123.3 + 0.1 is 123.3999999999 ?

[Simon Brunning]

> From:	Isaac To [SMTP:kkto at csis.hku.hk]
> Somehow people keep yelling that they can't stand the inaccuracy of
> floating
> points, without actually looking at how inaccurate (or actually, accurate)
> they are.
 
Ah, but try this:

>>> sum = 0.0
>>> for i in range(10): sum += 0.1
... 
>>> sum == 1
0

So, if you do any equality tests, even tiny inaccuracies can trip you up.
Using FixedPoint:

>>> import FixedPoint as fp
>>> sum = fp.FixedPoint(0.0)
>>> for i in range(10): sum += sum += 0.1
... 
>>> sum == 1
1

This works as expected.

Cheers,
Simon Brunning
TriSystems Ltd.
sbrunning at trisystems.co.uk




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