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Date: Wed, 3 Apr 2019 14:33:27 +0200
Message-ID: <CAG9XoMRC5cGQf+Q745MoO+pCP9MC57nkcuMfYZBj6iBdOHntvg@mail.gmail.com>
To: Michael Wallner <mike@php.net>, krakjoe@gmail.com, dafneves@gmail.com
Cc: PHP Internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] PHP_FLOAT_MIN is positive
From: benjamin.morel@gmail.com (Benjamin Morel)

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>
> It really don't make much sense:
> var_dump( PHP_FLOAT_MIN < 0 );
> var_dump( PHP_INT_MIN < 0 );


I quite agree that this is an inconsistency, but I guess that it's here to
stay now for BC reasons. What we can do is fix the doc.


> 2.2250738585072E-308
> This is negative.


It isn't, it is a strictly positive number with a negative exponent:
0.000(...)00022250738585072.

FLT_MIN is the smallest real near 0. Are you looking for -FLT_MAX?
> With IEEE754 floats, there are positive and negative zeros, so the range
> above and below 0 is the same.


It's interesting to know that - PHP_FLOAT_MAX is actually the smallest
representable floating point number (unlike - PHP_INT_MAX). It would be
great to document this as well.

I would propose to change the current documentation to:

PHP_FLOAT_MIN (float)
> Smallest representable POSITIVE floating point number. If you need the
> smallest representable floating point number, use - PHP_FLOAT_MAX.
> Available as of PHP 7.2.0.


What we could also do is introduce another constant to represent the actual
smallest possible float, but its naming would likely conflict with
PHP_FLOAT_MIN, and it does not bring much value, so I'm not sure whether
this is a good idea.
We did introduce a PHP_INT_MIN though, even though it was available as ~
PHP_INT_MAX, so it's worth mentioning.

Thoughts?



On Wed, 3 Apr 2019 at 13:50, Michael Wallner <mike@php.net> wrote:

> On 03/04/2019 12:27, Diogo Neves wrote:
> > It really don't make much sense:
> >
> > <?php
> >
> > var_dump( PHP_FLOAT_MIN < 0 );
> > var_dump( PHP_INT_MIN < 0 );
> >
> > On Wed, Apr 3, 2019 at 10:52 AM Benjamin Morel <benjamin.morel@gmail.com
> >
> > wrote:
> >
> >> Hi internals,
> >>
> >> I just used PHP_FLOAT_MIN for the first time, and was surprised that it
> is
> >> the smallest **positive** number representable. Is this expected?
> >>
> >> This is unlike PHP_INT_MIN, which is the absolute smallest representable
> >> integer, and as such is negative:
> >>
> >> echo PHP_INT_MIN; // -9223372036854775808
> >> echo PHP_FLOAT_MIN; // 2.2250738585072E-308
> >>
> >> If it is intended, maybe the doc
> >> <https://www.php.net/manual/en/reserved.constants.php> should be clear
> >> about this, at the moment it is just:
> >>
> >> Smallest representable floating point number.
> >>
> >>
> >> Which is confusing IMO.
>
> FLT_MIN is the smallest real near 0. Are you looking for -FLT_MAX?
> With IEEE754 floats, there are positive and negative zeros, so the range
> above and below 0 is the same.
>
>
> --
> Regards,
> Mike
>
>

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