On 13 November 2015 at 19:10, Jean-Pierre Flori <jpfl...@gmail.com> wrote:

>
>
> On Friday, November 13, 2015 at 9:40:27 AM UTC-8, Bill Hart wrote:
>>
>> Not in the published divide-and-conquer algorithm, no.
>>
>> There was a bug in the implementation of the new basecase algorithm,
>> which was not published, nor very important. On most machines it was
>> switched off. And even on the machines where it was used (with the
>> exception of itanium where it seemed to be used a lot), it was only used
>> for *very* small operands.
>>
>> To be verbose, do you mean the basecase schoolbook multiprecision
> division using 3by2 small division using a new 1 word precomputed inverse
> is broken?
>

Yes it was a 3by2 version using a new 1 word precomputed inverse (unrelated
to the 3by2 division originally used in MPIR and GMP).


> So is the code from BDSNT broken as wel?
> https://github.com/wbhart/bsdnt/blob/master/helper.c#L186
> https://github.com/wbhart/bsdnt/blob/master/nn_quadratic.c#L240
>
>
Doubtful. The implementation in MPIR was much, much more complex.

The algorithm itself is quite straightforward.

On the other hand, bsdnt does not have many users, so if bugs exist there,
it is much less likely they will be detected, so beware.

Bill.

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