Constants for better double edge case handling

8 years ago by Anatol Belski — view source

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Hi,

I would like to suggest adding the following constants

REGISTER_MAIN_LONG_CONSTANT("PHP_DBL_DIG", DBL_DIG, CONST_PERSISTENT |

CONST_CS);
REGISTER_MAIN_DOUBLE_CONSTANT("PHP_DBL_MAX", DBL_MAX, CONST_PERSISTENT |
CONST_CS);
REGISTER_MAIN_DOUBLE_CONSTANT("PHP_DBL_MIN", DBL_MIN, CONST_PERSISTENT |
CONST_CS);
REGISTER_MAIN_DOUBLE_CONSTANT("PHP_DBL_EPSILON", DBL_EPSILON,
CONST_PERSISTENT | CONST_CS);

The goal of this is to improve the handling of double in the user land. Here
are a couple of usages to illustrate the idea.

The comparison of double values.

$d0 = sin(M_PI/6.0);
$d1 = .5;
var_dump(
$d0, $d1,
abs($d0 - $d1),
$d0 == $d1,
abs($d0 - $d1) < PHP_DBL_EPSILON
);

float(0.5)
float(0.5)
float(5.5511151231258E-17)
bool(false)
bool(true)

The rounding behavior, max possible value representable by the string
conversion.

$d = .2345234523453245324323465;
echo $d, " ", round($d, 20), " ", round($d, PHP_DBL_DIG);

0.23452345234532 0.23452345234532 0.23452345234533

Producing INF. There's currently no explicit way to produce INF and NAN,
whereby NAN is gettable with sqrt(-1).

echo PHP_DBL_MAXPHP_DBL_MAX, " ", -PHP_DBL_MAXPHP_DBL_MAX;
INF -INF

In general, it is more about the possibility to handle the edge cases
properly. While such cases would cause unnecessary overhead and likely a BC
breach with a direct core implementation, they'd be fine to handle in the
scripts where it comes to it. I think, at least DBL_DIG and DBL_EPSILON
should be mapped to the constants, to provide a base for more flexibility.
The change itself is pretty outspoken, so I'm not sure it requires an RFC. I
would target at least master with this. Or 7.1, if RMs are ok.

Regards

Anatol

8 years ago by Kalle Sommer Nielsen — view source

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Hi Anatol

2016-10-18 20:46 GMT+02:00 Anatol Belski anatol.php@belski.net:

Hi,

I would like to suggest adding the following constants
REGISTER_MAIN_LONG_CONSTANT("PHP_DBL_DIG", DBL_DIG, CONST_PERSISTENT |
CONST_CS);
REGISTER_MAIN_DOUBLE_CONSTANT("PHP_DBL_MAX", DBL_MAX, CONST_PERSISTENT |
CONST_CS);
REGISTER_MAIN_DOUBLE_CONSTANT("PHP_DBL_MIN", DBL_MIN, CONST_PERSISTENT |
CONST_CS);
REGISTER_MAIN_DOUBLE_CONSTANT("PHP_DBL_EPSILON", DBL_EPSILON,
CONST_PERSISTENT | CONST_CS);

I like this idea but I do think that we should name them PHP_DOUBLE_*
or PHP_FLOAT_* (preferably the first).

--
regards,

Kalle Sommer Nielsen
kalle@php.net

8 years ago by Anatol Belski — view source

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Hi Kalle,

-----Original Message-----
From: kalle.php@gmail.com [mailto:kalle.php@gmail.com] On Behalf Of Kalle
Sommer Nielsen
Sent: Tuesday, October 18, 2016 9:05 PM
To: Anatol Belski anatol.php@belski.net
Cc: PHP Internals internals@lists.php.net; Davey Shafik davey@php.net; Joe
Watkins krakjoe@php.net
Subject: Re: [PHP-DEV] Constants for better double edge case handling

Hi Anatol

2016-10-18 20:46 GMT+02:00 Anatol Belski anatol.php@belski.net:
Hi,

I would like to suggest adding the following constants
REGISTER_MAIN_LONG_CONSTANT("PHP_DBL_DIG", DBL_DIG,
CONST_PERSISTENT | CONST_CS);
REGISTER_MAIN_DOUBLE_CONSTANT("PHP_DBL_MAX", DBL_MAX,
CONST_PERSISTENT | CONST_CS);
REGISTER_MAIN_DOUBLE_CONSTANT("PHP_DBL_MIN", DBL_MIN,
CONST_PERSISTENT | CONST_CS);
REGISTER_MAIN_DOUBLE_CONSTANT("PHP_DBL_EPSILON", DBL_EPSILON,
CONST_PERSISTENT | CONST_CS);
I like this idea but I do think that we should name them PHP_DOUBLE_* or
PHP_FLOAT_* (preferably the first).

Ah, indeed. PHP_FLOAT_* is what is consistent, probably.

Thanks

Anatol

8 years ago by Andrea Faulds — view source

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Hi Anatol,

Anatol Belski wrote:

Producing INF. There's currently no explicit way to produce INF and NAN,
whereby NAN is gettable with sqrt(-1).

echo PHP_DBL_MAXPHP_DBL_MAX, " ", -PHP_DBL_MAXPHP_DBL_MAX;
INF -INF

I'm not sure I understand this use-case. We already have the INF and NAN
constants for obtaining those values, and the standard IEEE 754
operations which produce these values are implemented (1/0 for INF, 0/0
for NAN, etc.)

--
Andrea Faulds
https://ajf.me/

8 years ago by Anatol Belski — view source

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Hi Andrea,

-----Original Message-----
From: Andrea Faulds [mailto:ajf@ajf.me]
Sent: Wednesday, October 19, 2016 2:49 PM
To: internals@lists.php.net
Subject: [PHP-DEV] Re: Constants for better double edge case handling

Hi Anatol,

Anatol Belski wrote:

Producing INF. There's currently no explicit way to produce INF and
NAN, whereby NAN is gettable with sqrt(-1).

echo PHP_DBL_MAXPHP_DBL_MAX, " ", -PHP_DBL_MAXPHP_DBL_MAX; INF
-INF

I'm not sure I understand this use-case. We already have the INF and NAN
constants for obtaining those values, and the standard IEEE 754 operations
which produce these values are implemented (1/0 for INF, 0/0 for NAN,
etc.)

Ah, so then it is fine, thanks for the education. Then it'd stay by DBL_DIG
and DBL_EPSILON. While DBL_MAX/ DBL_MIN could still be useful in some case
(fe one would want to explicitly know the values), in most case it'd be
covered by INF.

Regards

Anatol

8 years ago by Andrea Faulds — view source

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Hi,

Anatol Belski wrote:

Anatol Belski wrote:

Producing INF. There's currently no explicit way to produce INF and
NAN, whereby NAN is gettable with sqrt(-1).

echo PHP_DBL_MAXPHP_DBL_MAX, " ", -PHP_DBL_MAXPHP_DBL_MAX; INF
-INF

I'm not sure I understand this use-case. We already have the INF and NAN
constants for obtaining those values, and the standard IEEE 754 operations
which produce these values are implemented (1/0 for INF, 0/0 for NAN,
etc.)

Ah, so then it is fine, thanks for the education. Then it'd stay by DBL_DIG
and DBL_EPSILON. While DBL_MAX/ DBL_MIN could still be useful in some case
(fe one would want to explicitly know the values), in most case it'd be
covered by INF.

It can't hurt to add them anyway, though.

--
Andrea Faulds
https://ajf.me/