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Date: Tue, 4 Jun 2024 20:16:56 +0200
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Subject: Re: [PHP-DEV] [RFC] [discussion] Correctly name the rounding mode and
 make it an Enum
To: Derick Rethans <derick@php.net>, Saki Takamachi <saki@sakiot.com>
Cc: php internals <internals@lists.php.net>
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 <e4a8cf2e-fa63-e48d-5a99-d5d613313b50@php.net>
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From: tim@bastelstu.be (=?UTF-8?Q?Tim_D=C3=BCsterhus?=)

Hi

On 6/3/24 18:23, Derick Rethans wrote:
>> I would like to start an RFC discussion regarding rounding modes.
>> https://wiki.php.net/rfc/correctly_name_the_rounding_mode_and_make_it_an_enum
> 
> I think it would be really helpful to have a description (and examples)
> for each of the rounding modes in the Enum
> (https://wiki.php.net/rfc/correctly_name_the_rounding_mode_and_make_it_an_enum#proposal)
> — that'd also be great for creating documentation later on.

The `RoundingMode` enum will not provide any new rounding modes, thus 
the existing documentation of rounding modes applies. The corresponding 
constant names have been mentioned.

Nevertheless I've just added a PHPDoc with a brief definition and 
examples to each of the enum cases.

Please note: The definition is a little simplified to make it easier to 
understand the differences on a conceptual level.

It assumes arbitrary precision (which floats do not provide) and it 
assumes that rounding always rounds to integer values. In reality the 
round() function supports a specified number of decimal digits, with 
integer rounding being rounding to 0 decimal digits. An integer rounding 
function can emulate rounding to a specific number of decimal digits by 
multiplying the input value by 10**$digits, performing integer rounding, 
and then dividing by 10**$digits (assuming arbitrary precision).

There's also a helpful table on Wikipedia: 
https://en.wikipedia.org/wiki/Rounding#Comparison_of_approaches_for_rounding_to_an_integer

Hope this helps.

Best regards
Tim Düsterhus