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

[Nicolas Cellier]

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?
>>>>
>>>>
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