Re: [PHP] Strange Right-Shift Problem
Curt Zirzow wrote:
On Fri, Dec 30, 2005 at 12:34:35PM -0600, Richard Lynch wrote:
On Thu, December 29, 2005 5:37 pm, Michael Gross wrote:
...
If you can determine the number of bits on your system, you could use
a different number from 11 on the two systems to get the answer you
want.
if (is_32_bit_machine()){
$y = $x 11;
}
else{
$y = $x 43; //11 + 32 (guess)
}
One hack for detecting 32-bit machine might be this:
Isn't php suppose to handle all this? This seems odd to me.
I don't see how php can 'handle' people assuming that integers will
always be 32bits - the php code in the encryption algorythm is flawed
because it assumes that all integers are 32bits and doesn't platform
wordsize (terminology?) into account - how can php know that this was
not the intention?
Curt.
--
PHP General Mailing List (http://www.php.net/)
To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP] Strange Right-Shift Problem
On Fri, Dec 30, 2005 at 12:34:35PM -0600, Richard Lynch wrote:
On Thu, December 29, 2005 5:37 pm, Michael Gross wrote:
Hello
I have to migrate a PHP-application to a new Linux-Box. Both the old
and
the new system are Linux and PHP 5.1.1. (the old one has a Pentium 4,
the new one two Xeon CPUs). I have a problem using the
Crypt_Xtea-Extension. I narrowed it down to the following right-shift
operation:
(-3281063054 11) produces different results:
Old System: 495070
New System: -1048576
I understand that both results are wrong, but everything worked with
the old behavior and I need that behavior back very urgent.
Maybe someone can explain me in which way the bits are shifted so that
the result is 495070? If I understand it, I implement my own shift
function.
Assuming the previous hypothesis that it's 32-bit versus 64-bit
machines at work...
If you can determine the number of bits on your system, you could use
a different number from 11 on the two systems to get the answer you
want.
if (is_32_bit_machine()){
$y = $x 11;
}
else{
$y = $x 43; //11 + 32 (guess)
}
One hack for detecting 32-bit machine might be this:
Isn't php suppose to handle all this? This seems odd to me.
Curt.
--
cat .signature: No such file or directory
--
PHP General Mailing List (http://www.php.net/)
To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP] Strange Right-Shift Problem
Michael Gross wrote: Hello I have to migrate a PHP-application to a new Linux-Box. Both the old and the new system are Linux and PHP 5.1.1. (the old one has a Pentium 4, the new one two Xeon CPUs). I have a problem using the Crypt_Xtea-Extension. I narrowed it down to the following right-shift looking at the class I draw the conclusion that it reqires the use of [some] data in 'long' format (i.e. integers) and the code requires and assumes that such integers are 32bits long ... which they are on 32bit systems ... but not on 64bit systems . here in lies the problem, you need someone more knowledgable than I to give you an actual solution though. operation: (-3281063054 11) produces different results: Old System: 495070 this is what you get with a 32bit CPU New System: -1048576 this is what you get with a 64bit CPU I understand that both results are wrong, but everything worked with the old behavior and I need that behavior back very urgent. Maybe someone can explain me in which way the bits are shifted so that the result is 495070? If I understand it, I implement my own shift $a $b Shift left Shift the bits of $a $b steps to the left (each step means multiply by two) $a $b Shift right Shift the bits of $a $b steps to the right (each step means divide by two) function. thanks a lot Michael Gross -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP] Strange Right-Shift Problem
On Thu, December 29, 2005 5:37 pm, Michael Gross wrote:
Hello
I have to migrate a PHP-application to a new Linux-Box. Both the old
and
the new system are Linux and PHP 5.1.1. (the old one has a Pentium 4,
the new one two Xeon CPUs). I have a problem using the
Crypt_Xtea-Extension. I narrowed it down to the following right-shift
operation:
(-3281063054 11) produces different results:
Old System: 495070
New System: -1048576
I understand that both results are wrong, but everything worked with
the old behavior and I need that behavior back very urgent.
Maybe someone can explain me in which way the bits are shifted so that
the result is 495070? If I understand it, I implement my own shift
function.
Assuming the previous hypothesis that it's 32-bit versus 64-bit
machines at work...
If you can determine the number of bits on your system, you could use
a different number from 11 on the two systems to get the answer you
want.
if (is_32_bit_machine()){
$y = $x 11;
}
else{
$y = $x 43; //11 + 32 (guess)
}
One hack for detecting 32-bit machine might be this:
function is_32_bit_machine(){
return mt_getrandmax() == 0x;
}
I suppose if you're going to do this right, what you REALLY should do
is code it to determine the number of bits, no matter how large, and
then bit-shift the correct amount based on that.
So when the 128-bit machines come out in a few years, you aren't
re-coding this same damn problem AGAIN.
--
Like Music?
http://l-i-e.com/artists.htm
--
PHP General Mailing List (http://www.php.net/)
To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP] Strange Right-Shift Problem
Hello
Thanks for your answers. I now implemented everything new, with the
mcrypt-extension. However, I use the crypt_xtea still for a
compatibility mode. I had to implement the right-shift and other bit
operations. If someone is interested:
The problem occurred always when a number exceeded the 32bit and is
negative. The old behavior was to take 32bits and ignore the other bits
(therefore the sign could change in the rshift-operation). The following
simulates the old behavior:
function getbits($i) {
$bits = array();
while (abs($i) 1) {
$f1 = floor($i / 2.0);
$f2 = ceil($i / 2.0);
if ($f1!=$f2) {
array_push($bits, 1);
} else {
array_push($bits, 0);
}
$i = $f1;
}
return $bits;
}
function convertto32($i) {
$bits = getbits($i);
$i = 0;
if ($bits[ 0]) $i|=0x0001;
if ($bits[ 1]) $i|=0x0002;
if ($bits[31]) $i|=0x8000;
return $i;
}
function rshift($i, $n) {
if ($i -2147483648) {
$i = convertto32($i);
}
return $i $n;
}
thx
Michael Gross
Richard Lynch wrote:
On Thu, December 29, 2005 5:37 pm, Michael Gross wrote:
Hello
I have to migrate a PHP-application to a new Linux-Box. Both the old
and
the new system are Linux and PHP 5.1.1. (the old one has a Pentium 4,
the new one two Xeon CPUs). I have a problem using the
Crypt_Xtea-Extension. I narrowed it down to the following right-shift
operation:
(-3281063054 11) produces different results:
Old System: 495070
New System: -1048576
I understand that both results are wrong, but everything worked with
the old behavior and I need that behavior back very urgent.
Maybe someone can explain me in which way the bits are shifted so that
the result is 495070? If I understand it, I implement my own shift
function.
Assuming the previous hypothesis that it's 32-bit versus 64-bit
machines at work...
If you can determine the number of bits on your system, you could use
a different number from 11 on the two systems to get the answer you
want.
if (is_32_bit_machine()){
$y = $x 11;
}
else{
$y = $x 43; //11 + 32 (guess)
}
One hack for detecting 32-bit machine might be this:
function is_32_bit_machine(){
return mt_getrandmax() == 0x;
}
I suppose if you're going to do this right, what you REALLY should do
is code it to determine the number of bits, no matter how large, and
then bit-shift the correct amount based on that.
So when the 128-bit machines come out in a few years, you aren't
re-coding this same damn problem AGAIN.
--
PHP General Mailing List (http://www.php.net/)
To unsubscribe, visit: http://www.php.net/unsub.php
[PHP] Strange Right-Shift Problem
Hello I have to migrate a PHP-application to a new Linux-Box. Both the old and the new system are Linux and PHP 5.1.1. (the old one has a Pentium 4, the new one two Xeon CPUs). I have a problem using the Crypt_Xtea-Extension. I narrowed it down to the following right-shift operation: (-3281063054 11) produces different results: Old System: 495070 New System: -1048576 I understand that both results are wrong, but everything worked with the old behavior and I need that behavior back very urgent. Maybe someone can explain me in which way the bits are shifted so that the result is 495070? If I understand it, I implement my own shift function. thanks a lot Michael Gross -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
