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Subject: Re: [PHP-DEV] [RFC] [Discussion] Support object type in BCMath
In-Reply-To: <23c22396-4389-405a-ab24-b66070f58c01@alec.pl>
Date: Wed, 27 Mar 2024 09:36:52 +0900
Cc: internals@lists.php.net
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Message-ID: <9094EA74-584A-45EF-A887-5776F132C4BF@sakiot.com>
References: <4F094EDA-5058-407D-AF39-06FD934FDE1F@sakiot.com>
 <23c22396-4389-405a-ab24-b66070f58c01@alec.pl>
To: Aleksander Machniak <alec@alec.pl>
From: saki@sakiot.com (Saki Takamachi)

Hi Aleksander,

> Here's another question.
>=20
> 1. Since we have withScale(), do we need to inherit the $scale =
argument from the functional API? Can't we derive it from the object the =
method is being invoked on?
>=20
> So, instead, e.g.
>=20
> public function add(BcNum|string|int $num, ?int $scale =3D null): =
BcNum {}
> public function sqrt(?int $scale =3D null): BcNum {}
>=20
> I'd suggest:
>=20
> public function add(BcNum|string|int $num): BcNum {}
> public function sqrt(): BcNum {}
>=20
> but I have no clue about BCMath.

Yeah, you're right. By using `withScale` before calculating, we can =
obtain results of arbitrary precision without using Scale during =
calculation.

The code in that case would look like this:
```
$num =3D new Number('1.23');
$num2 =3D new Number('4.56');

$numRescaled =3D $num->withScale(4);

$result =3D $numRescaled->add($num2);
$result->value; // '5.7900'
$result->scale; // 4
```

On the other hand, if  allow the calculation method to specify a scale, =
we can write it like this:
```
$num =3D new Number('1.23');
$num2 =3D new Number('4.56');

$result =3D $num->add($num2, 4);
$result->value; // '5.7900'
$result->scale; // 4
```

It's just one less line, but that's the only reason to support the =
`$scale` argument.

However, for calculations other than mul and div, the calculation =
results will always fit within the scale.
```
$num =3D new Number('1.23'); // scale 2
$num2 =3D new Number('1'); // scale 0

$num->add($num2); // '2.23', scale 2 is enough
$num->sub($num2); // '0.23', scale 2 is enough
$num->mod($num2); // '0.23', scale 2 is enough
```

On the other hand, for mul, div, and pow, the original `$num` scale may =
not be enough.
```
$num =3D new Number('1.23'); // scale 2
$num2 =3D new Number('1.1'); // scale 1

$num->mul($num2); // '1.353' be '1.35', scale 2 is not enough
```

```
$num =3D new Number('1.23'); // scale 2
$num2 =3D new Number('4'); // scale 0

$num->div($num2); // '0.3075' be '0.30', scale 2 is not enough
$num->pow($num2); // '2.28886641', be '2.28' scale 2 is not enough
```

For mul and pow, can calculate the required scale. However, for div, the =
calculation may never end, such as `0.33333....`, so it is not possible =
to calculate the scale to fit the result completely.

In cases like this, we thought that some users would want to easily =
specify the scale, so we created an easy-to-use signature.

However, it may not be necessary to specify scale for all calculation =
functions. Is it reasonable to specify only mul, div, pow, or only div?

Regards.

Saki