Really Big Numbers Bug?

yeldarb

I'm having major headaches with 64-bit user ids that get passed in via an API. I have narrowed it down to 1 line that can reproduce the problem:

die(100000002568456);

That code results in the following being printed:
100000002568460

Is this a bug in PHP...? I have no idea why this would happen except for possibly something to do with 64 bit numbers. How do I get it to work correctly?

PHP version is 5.2.6, I know it's a few months out of date but it would really be a pain to upgrade PHP on these servers if I don't have to.

NogDog

From http://www.php.net/manual/en/language.types.integer.php:

The size of an integer is platform-dependent, although a maximum value of about two billion is the usual value (that's 32 bits signed). PHP does not support unsigned integers. Integer size can be determined using the constant PHP_INT_SIZE, and maximum value using the constant PHP_INT_MAX since PHP 4.4.0 and PHP 5.0.5.

If you need to deal with larger values as numbers, you will probably want to look into the [man]GMP[/man] or [man]BCMath[/man] extensions. If you just need to use them as IDs or such, use them as strings:

die('100000002568456');

yeldarb

Thanks for the reply NogDog, having them as strings would be perfectly acceptable for my purposes. I see now that they're getting converted to floats which, for User IDs obviously doesn't have the appropriate precision.

The problem is that the IDs are getting passed in by JSON and json_decode will apparently auto-convert these overflowed ints to floats. Is there a way to have it convert them to strings instead (I don't control the sending server)? I'm thinking maybe a tricky regex on the JSON I'm receiving at this point but hoping for a more elegant solution.

Weedpacket

While it feels like an evil hack, there is a workaround:

ini_set('precision', 15);

before decoding would disable display rounding enough for you to be able to cast it to a string intact (PHP's display default is 14 digits and your number has 15).

Assuming that the example ID number is accurate (if it's actually 16 digits long then the roundoff is real and not just for display, and poit goes the whole idea. Like I said: evil hack.)

yeldarb

Weedpacket;10918479 wrote:
While it feels like an evil hack, there is a workaround:
ini_set('precision', 15);
before decoding would disable display rounding enough for you to be able to cast it to a string intact (PHP's display default is 14 digits and your number has 15).

Assuming that the example ID number is accurate (if it's actually 16 digits long then the roundoff is real and not just for display, and poit goes the whole idea. Like I said: evil hack.)

I think their spec technically says it's an unsigned 64 bit number so that would only be a stopgap measure for a while. But I am pretty sure they are now going sequentially so who knows if they will ever use that last bit. Better to be safe than sorry though; I am now just extracting them from the JSON myself using String manipulation rather than json_decode.

Thanks guys for all the help.

dalecosp

[501] Thu 18.Jun.2009 12:28:48
[kadmin@somehost][~]
php -r "die(100000002568456);"
1.0000000256846E+14