Newsgroups: php.internals
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Date: Tue, 9 Apr 2024 11:52:57 +0100 (BST)
To: Alex Pravdin <alex.pravdin@interi.co>
cc: internals@lists.php.net
Subject: Re: [PHP-DEV] Proposal: Arbitrary precision native scalar type
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From: derick@php.net (Derick Rethans)

On Thu, 7 Dec 2023, Alex Pravdin wrote:

> Accounting for all of the above, I suggest adding a native numeric 
> scalar arbitrary precision type called "decimal". Below are the 
> preliminary requirements for implementation.

Adding a new native type to PHP will create a large change. Not only is 
it "just" adding a new native type, it also means all of the conversions 
between types need to be added. This is not a small task.

> Decimal values can be created from literals by specifying a modifier or using
> the (decimal) typecast:
> 
> $v = 0.2d;
> $v = (decimal) 0.2; // Creates a decimal value without intermediary float
> 
> It uses the precision and scale defined in php.ini.

If you want to use arbitrary precision natives, then a precision and 
scale as defined in php.ini defeats the purpose. Every installation can 
then potentially calculate things in a different way.

The only way how to prevent that, is to have *actual* Decimal type, such 
as the Decimal type in MongoDB uses (the IEEE 754 decimal128 type):

- https://www.mongodb.com/docs/mongodb-shell/reference/data-types/#std-label-shell-type-decimal
- https://en.wikipedia.org/wiki/Decimal128_floating-point_format

cheers,
Derick

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