ID: 16366
Updated by: [EMAIL PROTECTED]
Reported By: [EMAIL PROTECTED]
Status: Open
Bug Type: Math related
Operating System: WinXP
PHP Version: 4.1.2
New Comment:
Actually - the echo(11>>34) issue, is somewhat expected behavior. What
happens, is that it returns 11>>2 (34 - 32) - BUT only on a 32-bit
system.
I just checked at an AIX 64-bit system, and there echo(11>>34) gives 0
And anything above 64-bit is than equal to $int>>($shift % 64).
Maybe it should be added to the bitwise operators documentation.
<?php
print("32 bits test\n");
$int=11;
for ($shift=31;$shift<35;$shift++)
{
print("$shift: ");
$check=$int>>$shift;
print($check);
print("\n\n");
}
print("64 bits test\n");
for($shift=63;$shift<67;$shift++)
{
print("$shift: ");
$check=$int>>$shift;
print($check);
print("\n");
}
?>
On a 64-bit system produces:
$ php -f test.php
32 bits test
31: 0
32: 0
33: 0
34: 0
64 bits test
63: 0
64: 11
65: 5
66: 2
On a 32-bit system produces:
32 bits test
31: 0
32: 11
33: 5
34: 2
64 bits test
63: 0
64: 11
65: 5
66: 2
Previous Comments:
------------------------------------------------------------------------
[2002-03-31 13:42:14] [EMAIL PROTECTED]
Just a reminder of the original issue:
echo (11>>34) produces "2"
This is not a documentation problem, unless you want to write that
shifting greater than 32 has incorrect results.
------------------------------------------------------------------------
[2002-03-31 13:39:23] [EMAIL PROTECTED]
are you sure? there is already a bunch of reports on "floating-point
bugs" in PHP. That's why I didn't reopen it.
------------------------------------------------------------------------
[2002-03-31 13:38:51] [EMAIL PROTECTED]
Well I have 200 groups of 64 on/off's.. I can name the 200 bigint
groups but there is no way in hell I am going to name 12,800 bools, not
to mention that they would take up 8x more space in the database.. Each
group has the same structure - somebody needs to write a DB that uses
structures as custom fields. This may be the way they work but this is
ancient design - I was surprised as hell when I started learning MySQL
and realized that they are still doing things this way. But anyway.
Now I am thinking "char binary" since it can be fixed size, but the
documentation on PHP's conversions of MySQL is sparse. If someone
would like to pursue this in private email please write.
The original bug was about bit shifting, which I don't think would
involve a conversion to float.. unless PHP is doing something weird.
It looks like someone is just not expecting a shift greater than 32.
------------------------------------------------------------------------
[2002-03-31 13:27:30] [EMAIL PROTECTED]
Good point. Reopening as documentation problem.
------------------------------------------------------------------------
[2002-03-31 13:23:52] [EMAIL PROTECTED]
Related to the bug only:
<?php
$int=2;
for($i=25;$i<33;$i++)
{
$check=pow($int, $i);
$check2=(int)$check;
$check2 += 1;
$check3=(int)$check;
$check3 -= 1;
echo("i is $i\n");
var_dump($check);
var_dump($check2);
var_dump($check3);
echo("\n");
}
?>
Gives some weird results:
$ ./test_float_conversion.php
i is 25
int(33554432)
int(33554433)
int(33554431)
i is 26
int(67108864)
int(67108865)
int(67108863)
i is 27
int(134217728)
int(134217729)
int(134217727)
i is 28
int(268435456)
int(268435457)
int(268435455)
i is 29
int(536870912)
int(536870913)
int(536870911)
i is 30
int(1073741824)
int(1073741825)
int(1073741823)
i is 31
float(2147483648)
int(-2147483647)
float(-2147483649)
i is 32
float(4294967296)
int(1)
int(-1)
I guess the manual should be appended, in the 'typecasting' section, to
not cast to integer, when it's larger than 2^30 and that those numbers
are automatically converted to floats.
(http://www.php.net/manual/en/language.types.type-juggling.php#language.types.typecasting)
------------------------------------------------------------------------
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