[issue] Representing nonterminating binary float results
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Hey, what a great idea! We should do this too. :-)
I believe that the Python license is sufficient flexible that we can
Steal This Code! if anybody wants to work on it.
P.S. If I set up the subject correctly, this should appear on the
tracker shortly.
Nick Coghlan writes:
On 2 December 2013 11:45, Mark Lawrence
<breamoreboy(a)yahoo.co.uk> wrote:
> The newbie says it should be 4.5 but gets 4.499999999999999999999 so raises
> issue on bug tracker stating that Python can't do arithmetic properly.
>
> In [5]: 9/2
> Out[5]: 4.5
>
> Blast, lousy example :)
Getting a modern Python to fall into that trap at all is actually
quite difficult - the way str.__repr__ works was changed a while ago
to favour the nearest terminating approximation that is represented
using the same IEEE754 bit pattern :)
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>>>> "Stephen" == Stephen J Turnbull
<stephen(a)xemacs.org> writes:
Stephen> Hey, what a great idea! We should do this too. :-)
Stephen> I believe that the Python license is sufficient flexible that we can
Stephen> Steal This Code! if anybody wants to work on it.
Stephen> P.S. If I set up the subject correctly, this should appear on the
Stephen> tracker shortly.
FWIW, Dybvig has a paper on printing floats. Dybvig includes a full
scheme implementation in the paper and provides a C implementation as
well. I think the C implementation is missing one of the algorithms
in the paper, however. I think the implementation needs bignum
arithmetic.
Ray
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Raymond Toy <toy.raymond(a)gmail.com> writes:
>>>>> "Stephen" == Stephen J Turnbull
<stephen(a)xemacs.org> writes:
Stephen> Hey, what a great idea! We should do this too. :-)
Stephen> I believe that the Python license is sufficient flexible that we can
Stephen> Steal This Code! if anybody wants to work on it.
Stephen> P.S. If I set up the subject correctly, this should appear on the
Stephen> tracker shortly.
FWIW, Dybvig has a paper on printing floats. Dybvig includes a full
scheme implementation in the paper and provides a C implementation as
well. I think the C implementation is missing one of the algorithms
in the paper, however. I think the implementation needs bignum
arithmetic.
No, Bob Burger's algorithm comes with its own, very restricted implementation of
bignum arithmetic. It takes a little work as it only represents the
digits, but otherwise is quite operational.
--
Regards,
Mike
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Michael Sperber -
Raymond Toy -
Stephen J. Turnbull