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

[Nicolas Cellier]

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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