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Date: Sun, 9 Feb 2025 14:45:00 +0100
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Subject: Re: [PHP-DEV] Introduction - Sam Lewis
To: Eugene Sidelnyk <zsidelnik@gmail.com>, Sam Lewis <sam.lewis0602@gmail.com>
Cc: Rob Landers <rob@bottled.codes>, PHP Internals <internals@lists.php.net>
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From: tim@bastelstu.be (=?UTF-8?Q?Tim_D=C3=BCsterhus?=)

Hi

On 2/8/25 20:52, Eugene Sidelnyk wrote:
> Maybe there could be another good feature to start with - the function to
> format bytes into a human-readable format (for debug purpuses) to have
> pretty view of the size (like 1.5GB, or 20MB)
> 
> […]
> 
> This is too little thing for having separate composer library, and perhaps
> having it built-in would be better?

On a surface level such a function would appear to be very simple, but 
the “human-readable format” bit alone already raises multiple questions, 
with the most notable one being: What is human-readable?

There's different languages in the world and they all use different 
decimal separators and group digits differently. And they possibly have 
different rules with regard to whether or not a space is required 
between the scalar part and the unit. In fact your example already is 
*incorrect* English, because English requires a space between the scalar 
part and the unit. And it should ideally be a non-breaking space.

So in English it would be:

- 1.5 GB
- 20 MB

In German we use the comma as the decimal separator (and also a space 
before the unit), so it would need to be:

- 1,5 GB
- 20 MB

Then there's also the question of whether to use the binary scale or the 
decimal scale. In other words: Should 1460 Bytes be rendered as 1.5 kB 
or as 1.4 KiB?

Also: How many decimal digits should be printed? Should it even be a 
fixed number of decimal digits, or are we rather interested in a total 
number of significant digits? In more explicit terms:

For 2 *decimal* digits:

1234 Bytes   -> 1.23 kB
12345 Bytes  -> 12.35 kB
123456 Bytes -> 123.46 kB

For 3 *significant* digits:

1234 Bytes   -> 1.23 kB
12345 Bytes  -> 12.3 kB
123456 Bytes -> 123 kB

Then there's the question of when the next unit should be used. Should 
the cut-off point be “there needs to be a 1 in front of the decimal 
point”? In some cases printing 0.9 GB might be preferable to 900 MB.

I could probably go on and find further questions, but I believe this 
already showcases how the devil is in the details - as with many RFCs 
that look great on a surface level.

In this specific case of usefully formatting numbers, I can recommend 
taking a look at the NumberFormatter class of ext/intl 
(https://www.php.net/manual/en/class.numberformatter.php). The API is 
not particularly pretty, but it handles the complex details of 
“correctly formatting a float according to language rules”. AFAICT you 
would still need to append the correct unit (and divide the number of 
bytes) yourself, though.

Best regards
Tim Düsterhus