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Subject: Re: [PHP-DEV] Add bcdivmod() to BCMath
Date: Wed, 26 Jun 2024 01:29:58 +0900
Message-ID: <0E1E1C82-24A2-46FF-B649-56DD7C39350D@sakiot.com>
References: <190502bc4bf.1145fe1df199171.9215746182322416249@barneylaurance.uk>
Cc: php internals <internals@lists.php.net>
In-Reply-To: <190502bc4bf.1145fe1df199171.9215746182322416249@barneylaurance.uk>
To: Barney Laurance <barney@barneylaurance.uk>
From: saki@sakiot.com (Saki Takamachi)

Thanks all,

> My only question is the pseudo-tuple return, which is rarely used in PHP (=
although I've used it myself, I think exactly once), and I think this would b=
e the first use of it in a built in library.  (I may be wrong on that.)  I d=
on't have a particular alternative to suggest, just flagging that as the mai=
n part that could warrant discussion.


> It's actually already used by gmp_div_qr(), so +1 from me.

I predicted this would probably be on the agenda. Another idea is to pass ar=
guments by reference, like in `exec()`.

Personally, I find something like a tuple easier to use. However, without ge=
nerics, all we know is that the return type is an array, which may be inconv=
enient in terms of IDE completion, etc.

> I'm wondering whether this needs to be a change to the API, or if it might=
 be better implemented as a purely internal optimisation to BCMath / Number -=
 in some way memoize both the quotient and the remainder when either div or m=
od is called, and then document for users that calling one after the other w=
ill be extremely cheap to run.
>=20
> But maybe that brings up too many questions about memory usage - e.g. is t=
he memory for this reserved in advance for each instance of Number, or alloc=
ated when one of these functions is called, and should it be freed even whil=
e the object remains in scope to avoid using lots of memory if many numbers a=
re divided or modded.

I am considering implementing this not only as a Number class, but also as a=
 function.

Also, it is not practical to record the remainder in the Number object resul=
ting from the division. This is because there can be objects whose division r=
esults are equal but whose remainders are different.

In the discussion of the Number class, it was argued that objects should not=
 have too much state.=20

Increasing the state of surplus is not desirable in this respect, as it cont=
radicts the previous argument.

Regards,

Saki=