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Re: Strange bug
From: |
Gaute B Strokkenes |
Subject: |
Re: Strange bug |
Date: |
17 Jan 2001 20:12:47 +0000 |
User-agent: |
Gnus/5.0803 (Gnus v5.8.3) Emacs/20.7 |
On Wed, 17 Jan 2001, hacksaw@FISHFISHFISHhacksaw.org wrote:
> Hacksaw wrote:
>
>> (+ 20.00 9.99 9.99 18.00 11.99 9.99 9.99 3.25 3.00 9.99 18.00 9.99
>> 11.50 9.99)
>> 155.67000000000002
>>
>> GNU Emacs 20.5.1 (i386-redhat-linux-gnu, X toolkit) of Mon Feb 21
>> 2000 on porky.devel.redhat.com
>>
>> glibc-2.1.3-15
>>
>> RH 6.2
>
> Two people have written me saying this is a precision error that is
> to be expected.
>
> Folks, precision errors happen at the ends of arrays, not the
> beginning.
Sorry?
> Also, I'm ADDING. Precision errors typically happen on division or
> multiplication. (Mostly just division).
>
> The only computational error one could expect on adding is overflow.
You are very wrong. Find yourself a good book about numerical
analysis if you're interested. There are *lots* of pitfalls when it
comes to computer floating point arithmetic.
> Further replies may be posted to the newsgroup, which I am now
> monitoring.
I haven't made a thorough analysis of the specific problem you're
having, but one thing to keep in mind is that although a number may be
written exactly in decimal floating point format does not necessarily
mean that it can be written exactly as a binary floating point number
with a fixed-size mantissa. For instance, I can write the fraction
1/3 exactly in tertiary floating point as 0.1 . In decimal, it is
impossible to represent that number exactly using only a finite number
of digits, since the best you can do is 0.33333333... with a finite
number of 3's. There are numerous other possible causes for your
problem as well.
--
Gaute Strokkenes http://www.srcf.ucam.org/~gs234/
I like the way ONLY their mouths move.. They look like DYING OYSTERS
- Strange bug, Hacksaw, 2001/01/15
- Re: Strange bug, Hacksaw, 2001/01/17
- Re: Strange bug,
Gaute B Strokkenes <=
- Re: Strange bug, Hacksaw, 2001/01/19
- Re: Strange bug, Colin Walters, 2001/01/19
- Re: Strange bug, Deepak Goel, 2001/01/20
- Re: Strange bug, Mark H. Weaver, 2001/01/21
- Re: Strange bug, Mark H. Weaver, 2001/01/22
- Re: Strange bug, thi, 2001/01/17