PHP_FLOAT_MIN is positive

6 years ago by Benjamin Morel — view source — reply

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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.

Cheers,
Ben

6 years ago by Diogo Neves — view source — reply

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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.

Cheers,
Ben

6 years ago by Joe Watkins — view source — reply

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2.2250738585072E-308

This is negative.

Cheers
Joe

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.

Cheers,
Ben

6 years ago by Michael Wallner — view source — reply

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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

6 years ago by come@opensides.be — view source — reply

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Le mercredi 3 avril 2019, 13:47:55 CEST Joe Watkins a écrit :

2.2250738585072E-308

This is negative.

Cheers
Joe

No it’s not.
It’s positive and close to 0.

Côme

6 years ago by Benjamin Morel — view source — reply

unread

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?

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

6 years ago by Claude Pache — view source — reply

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Le 3 avr. 2019 à 11:51, Benjamin Morel benjamin.morel@gmail.com a écrit :

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.

Cheers,
Ben

And in order to avoid further confusion, the constant ought to be renamed PHP_FLOAT_MIN_POSITIVE.

Rust named it correctly: https://doc.rust-lang.org/std/f64/constant.MIN_POSITIVE.html https://doc.rust-lang.org/std/f64/constant.MIN_POSITIVE.html

—Claude

6 years ago by Rowan Collins — view source — reply

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On Wed, 3 Apr 2019 at 13:33, Benjamin Morel benjamin.morel@gmail.com
wrote:

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.

I'd avoid the word "smallest". PHP_FLOAT_MIN could be described as having
the "smallest magnitude", and -PHP_FLOAT as being "the largest magnitude,
but negative".

Perhaps:

Closest representable positive floating point number to zero. If you need
the
negative number furthest from zero, use -PHP_FLOAT_MAX.

Regards,

Rowan Collins
[IMSoP]

6 years ago by Joe Watkins — view source — reply

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Thanks for explain.

Cheers
Joe

On Wed, 3 Apr 2019 at 13:33, Benjamin Morel benjamin.morel@gmail.com
wrote:

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.

I'd avoid the word "smallest". PHP_FLOAT_MIN could be described as having
the "smallest magnitude", and -PHP_FLOAT as being "the largest magnitude,
but negative".

Perhaps:

Closest representable positive floating point number to zero. If you need
the
negative number furthest from zero, use -PHP_FLOAT_MAX.

Regards,

Rowan Collins
[IMSoP]

6 years ago by Sara Golemon — view source — reply

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On Wed, Apr 3, 2019 at 4:52 AM Benjamin Morel benjamin.morel@gmail.com
wrote:

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.

Perhaps confusing, but not without precedent. See the C++ definitions for
::min() and ::lowest() on
https://en.cppreference.com/w/cpp/types/numeric_limits.

std::numeric_limits<double>::min() is a positive value very near zero.
std::numeric::limits<double>::lowest() is a very large negative value.

-Sara