Re: [PHP-DEV] [RFC] [Discussion] Rounding Integers as int

[Marc Bennewitz]

Hi Larry,

On 10.03.24 16:52, Larry Garfield wrote:

On Sun, Mar 10, 2024, at 10:31 AM, Gina P. Banyard wrote:

On Saturday, 9 March 2024 at 16:00, Larry Garfield
<la...@garfieldtech.com> wrote:

I am still opposed to this. Logically, ceil/float/round should be returning 
ints, not floats. Only returning ints if it was given an int is, er, kinda 
pointless, as you'll just get back the value you passed in. (Because it's 
already rounded/floored, etc.) So this doesn't get us any new type safety, but 
does make the return type less consistent than it is today. That's a step 
backwards.

If there's some math reason that we cannot have those functions return int (someone 
mentioned there was, but I don't really understand it and the RFC does not explain it at 
all), then we should at least keep consistency in the return type. "Sometimes I have 
to cast the return value before I can actually use it in the obvious way, sometimes I 
don't" is not a good situation.

--Larry Garfield

There are plenty of values that are exactly representable as floating
point numbers but not as integers.

One short example:

$v = 1e10 + 0.6;
var_dump($v);
var_dump(round($v));

Gives you accurate precision and proper rounding behaviour.

1e10 *cannot* be represented as an integer.

So round *must* be able to return a float.

Best regards,

Gina P. Banyard

Please include some version of this in the RFC.  Especially if it can be even 
more detailed.

--Larry Garfield

In case you where looking at python where round() is documented with ...






I have added a description and updated example in the RFC.


Best,
Marc

While float's get imprecise on represent integers > 2^53, int's can't represent such a bit range of numbers as floats can. On rounding a floating point number your already have to deal with the imprecise of floats in the first place. That's why rounding operations should take the input type into account and only cast if the input type can't represent the resulting number to avoid ending up in overflow or error. > The return value is an integer if /ndigits/ is omitted or |None|. Otherwise, the return value has the same type as /number/. ... but in python int is limited only by memory and not by the type which makes it very different.

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