[Cuis-dev] Bug in Integer>>#raisedTo:modulo:

[Luciano Notarfrancesco]

Makes sense, thank you!

On Mon, 5 Jun 2023 at 19:11 Nicolas Cellier <
nicolas.cellier.aka.nice at gmail.com> wrote:

> I replaced ALL sends, not just this one, because it's putting too much
> responsibility for senders for a very weak gain
>
> Le lun. 5 juin 2023 à 19:09, Luciano Notarfrancesco <luchiano at gmail.com>
> a écrit :
>
>> Ah, good to know, you replaced all calls to \\\ with \\ in all methods or
>> only this one? We should do the same in Cuis. Still, the randomness mystery
>> remains…
>>
>> On Mon, 5 Jun 2023 at 19:04 Nicolas Cellier via Cuis-dev <
>> cuis-dev at lists.cuis.st> wrote:
>>
>>> Ah OK... I expunged the sends of \\\ operator from Squeak.
>>> This is exactly like \\ but omits normalization of LargeInteger result...
>>> Below is the comment that i let in \\\ definition:
>>>
>>>
>>> "A modulo method former used in DSA."
>>>
>>> "Notes: this method used to be a faster than \\ for LargeIntegers, but
>>> this advantage is fainting:
>>> - it always was slower for SmallInteger because of the indirection below
>>> - a new LargeInteger primitive makes \\ faster up to 64 bits operands
>>> - even above 64 bits, its advantage has become marginal thanks to
>>> revised \\ primitive fallback code
>>> Moreover, \\\ behaviour is questionable for these reasons:
>>> - for a negative receiver xor argument, it behaves like rem: for
>>> LargeInteger and \\ for SmallInteger
>>> - it may answer a not normalized LargeInteger (with leading null digits)
>>> which breaks some invariants
>>> For example, check (SmallInteger maxVal + 1 \\\ 8) isZero.
>>> So beware if you ever think using this method."
>>>
>>>
>>> Le lun. 5 juin 2023 à 18:56, Luciano Notarfrancesco via Cuis-dev <
>>> cuis-dev at lists.cuis.st> a écrit :
>>>
>>>> Doing
>>>>     pow := pow * pow \\ m
>>>> instead of
>>>>     pow := pow * pow \\\ m
>>>> at the beginning of the loop in
>>>> Integer>>#slidingLeftRightRaisedTo:modulo: seems to fix it. But still I’m
>>>> not sure why it is random otherwise, and I’m not sure that this really
>>>> fixes the problem.
>>>>
>>>>
>>>> On Mon, 5 Jun 2023 at 18:42 Luciano Notarfrancesco <luchiano at gmail.com>
>>>> wrote:
>>>>
>>>>> The following:
>>>>>     5445648384 raisedTo: 3 modulo: 1 << 34
>>>>> Returns 0, which is right. But
>>>>>     5445648384 raisedTo: 4 modulo: 1 << 34
>>>>> Returns different numbers every time I call it (it should return 0).
>>>>> It’s very weird… I don’t see where the randomness is coming from,
>>>>> perhaps from LargeIntegerPlugin?
>>>>>
>>>>>
>>>>> --
>>>> Cuis-dev mailing list
>>>> Cuis-dev at lists.cuis.st
>>>> https://lists.cuis.st/mailman/listinfo/cuis-dev
>>>>
>>> --
>>> Cuis-dev mailing list
>>> Cuis-dev at lists.cuis.st
>>> https://lists.cuis.st/mailman/listinfo/cuis-dev
>>>
>>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.cuis.st/mailman/archives/cuis-dev/attachments/20230605/b2041fc8/attachment-0001.htm>