Bug #50080 [Nab]: 1 bit short of an 8 byte integer
Edit report at https://bugs.php.net/bug.php?id=50080&edit=1
ID: 50080
Updated by: rasmus@php.net
Reported by: aidevelopment at gmail dot com
Summary: 1 bit short of an 8 byte integer
Status: Not a bug
Type: Bug
Package: Variables related
Operating System: Linux 2.6.15-26-server
PHP Version: 5.2.11
Block user comment: N
Private report: N
New Comment:
It is quite clearly stated in the documentation exactly where you would expect it
to be at http://php.net/types where it says:
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). 64-bit platforms usually
have a maximum value of about 9E18. PHP does not support unsigned integers.
Previous Comments:
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[2013-06-02 22:10:08] gustav at svalander dot eu
If PHP does not support uint64 then it should be clearly stated in the
documentation. This crap cost me 8h.
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[2009-11-05 01:56:01] aidevelopment at gmail dot com
Hi Jani,
Thanks for the update. Please, allow me to clarify my last post.
With the information you've given, we know the 64th bit (far left), is reserved for sign.
With a simple two line script, we can see that 0 = positive, therefore 1 = negative.
//determine positive vs. negative (observe far left bit).
$a=5;
printf("a = '%b'", $a);
The example below will show the difference between actual expected result when increasing integers
past the maximum value of an unsigned int.
//set a equal to the max
$a = 0x7FFFFFFFFFFFFFFF;
//add one
$a++;
//Expecting a variable wrap here. e.x. $a = -0x7FFFFFFFFFFFFFFF
//Actual result is $a = negative 0
printf("a = '%b'", $a);
//add one
$a++;
//Given a is now actually equal to negative 0
//Expecting a = 1;
//Actual result is $a = negative 0 (unchanged).
printf("a = '%b'" ,$a);
I would appreciate if you would explain how giving the incorrect answer to a simple mathematical
formula (x+1) is not a bug. If this is in fact a bug, please re-open, reassign and/or recategorize
this bug appropriately. Thanks!
Cheers!
Steve
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[2009-11-04 22:51:22] jani@php.net
No.
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[2009-11-04 17:59:05] aidevelopment at gmail dot com
I understand what you are saying. However, the handling is very difficult to understand. As you can
see, adding 1 simply has no effect past positive 0
(1000000000000000000000000000000000000000000000000000000000000000). I have not been able to
determine yet exactly what happens when you explicitly assign a variable to a value "too
large".
Is there no way to have PHP utilize 64 bit values (uint64)?
------------------------------------------------------------------------
[2009-11-04 17:17:58] sjoerd@php.net
In a 64 bit integer, 1 bit indicates the sign and 63 bits are left for the number. Thus the range is
from -2^63 to 2^63, giving 2^64 numbers.
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