Edit report at https://bugs.php.net/bug.php?id=50080&edit=1
ID: 50080
Comment by: gustav at svalander dot eu
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:
If PHP does not support uint64 then it should be clearly stated in the
documentation. This crap cost me 8h.
Previous Comments:
------------------------------------------------------------------------
[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
------------------------------------------------------------------------
[2009-11-04 22:51:22] [email protected]
No.
------------------------------------------------------------------------
[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] [email protected]
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.
------------------------------------------------------------------------
[2009-11-04 16:14:21] aidevelopment at gmail dot com
Description:
------------
Despite having PHP_INT_MAX set to 8 bytes, It is impossible to have an int
greater than 1000000000000000000000000000000000000000000000000000000000000000.
8 Byte, or 64 bit maximum should be
1111111111111111111111111111111111111111111111111111111111111111.
In my included example, it is clear that when attempting to increase the value
above(by adding 1), simply nothing happens.
Attempting to assign a variable to a number greater than the above number
produces unpredictable results.
Reproduce code:
---------------
<?php
echo "Int Size = ".PHP_INT_SIZE." bytes.<br>";
$status = 0x7FFFFFFFFFFFFFFF;
for($i=0;$i<=4;$i++)
{
printf ("status = '%b'<br>", $status);
$status++;
}
?>
Expected result:
----------------
Int Size = 8 bytes.
status = '111111111111111111111111111111111111111111111111111111111111111'
status = '1000000000000000000000000000000000000000000000000000000000000000'
status = '1000000000000000000000000000000000000000000000000000000000000001'
status = '1000000000000000000000000000000000000000000000000000000000000010'
status = '1000000000000000000000000000000000000000000000000000000000000011'
Actual result:
--------------
Int Size = 8 bytes.
status = '111111111111111111111111111111111111111111111111111111111111111'
status = '1000000000000000000000000000000000000000000000000000000000000000'
status = '1000000000000000000000000000000000000000000000000000000000000000'
status = '1000000000000000000000000000000000000000000000000000000000000000'
status = '1000000000000000000000000000000000000000000000000000000000000000'
------------------------------------------------------------------------
--
Edit this bug report at https://bugs.php.net/bug.php?id=50080&edit=1
