ID: 29874
User updated by: binhqx at mac dot com
-Summary: Bitwise right shift operator produces incorrect
result.
Reported By: binhqx at mac dot com
Status: Open
Bug Type: *Math Functions
Operating System: OS X Server 10.3 (Darwin 7.5.0)
PHP Version: Irrelevant
New Comment:
I did some digging in the code using gdb and found the
root of the problem likly resides in
zend_operators.c in shift_right_function().
On line 1108 of zend_operators.c the
zendi_convert_to_long macro is called then the
DVAL_TO_LVAL macro.
To me, it looks like inconsistency occurs here:
zend_operators.c:186
#define DVAL_TO_LVAL(d, l) (l) = (d) > LONG_MAX ?
(unsigned long) (d) : (long) (d)
When d is greater then LONG_MAX, d is cast as a unsigned
long. When the value is then copied into
op1_copy.value.lval, it is recast as to a long.
The bug appears to be with the OS.
Here is some code to show the inconsistency:
--------------
#include <iostream>
using namespace std;
int main (int argc, char * const argv[]) {
double large_number = 8e10;
cout << "Casting Test\n";
cout << "double = " << large_number
<< "\n";
cout << "unsigned long = " << (unsigned long
int)large_number << "\n";
cout << "long = " << (long int)(unsigned
long int)large_number << "\n";
return 0;
}
--------------
OS X result:
--------------
Casting Test
double = 8e+10
unsigned long = 4294967295
long = -1
Linux result:
--------------
Casting Test
double = 8e+10
unsigned long = 2690588672
long = -1604378624
It looks like this is a OS X bug rather then a PHP bug.
Does any one know of workaround code to make OS X act
like Linux in PHP or C?
Previous Comments:
------------------------------------------------------------------------
[2004-08-28 06:50:59] binhqx at mac dot com
I did some more searching through the bug archive and
found many bugs pertaining to logic operator and
doubles.
Before I get redirected to one of those, I would like to
emphasize that this is not a problem with the value
being produced. The problem is the same operation is
producing different results on different platforms.
------------------------------------------------------------------------
[2004-08-28 06:35:30] binhqx at mac dot com
Original description was cutoff:
Bitwise right shift operator produces incorrect result
when applied to a double in all version of PHP on OS X.
During a bitwise right shift, the php processor casts
the operand to a integer. Most of the time this works
fine, but when the value of the operand is greater the
32 bits, the variable is chopped to just the last 32
bits. This is the way it should work.
For example: 136586474 >> 10 becomes 133385
Under OS X Server, this casting procedure does not work
the same way. When value of the operand is greater then
32
bits, the variable is changed to the largest posable
value of a integer (2^32). Because all integers are
signed
this is -1. 8726521066 >> 10 becomes -1
I have tested the the shift operator on Linux using PHP
4.1.2 - 4.3.4 and it produces the correct results. On OS
X/OS X Server (Darwin 7.5.0) using PHP 4.3.2 - 5.0.1 and
it produces the incorrect results.
It would appear the bug only exists in the OS X port of
PHP.
Examples:
Testing OS X Server: http://worldvoicellc.net/
bitshift_test.php
Testing Linux: http://12.160.216.20/altigen/phptest/
bitshift_test.php
Testing code: http://worldvoicellc.net/bitshift_test.txt
------------------------------------------------------------------------
[2004-08-28 06:27:42] binhqx at mac dot com
Description:
------------
Bitwise right shift operator produces incorrect result
when applied to a double in all version of PHP on OS X.
During a bitwise right shift, the php processor casts
the operand
Reproduce code:
---------------
$operand = 8726521066;
echo ($operand >> 10);
Expected result:
----------------
133385
Actual result:
--------------
-1
------------------------------------------------------------------------
--
Edit this bug report at http://bugs.php.net/?id=29874&edit=1
