STrange error (bitwise operation)

[gorros]

I have implemented a encrypt/decrypt algorithm (original in javascript), and when looping I got strange result.

As a test I just made a quick printout at a known value of one of the parameters.

 

This is the local code

 

$z = $v[$p-1];

$ii= 4071400299;

if ($ii==$z){

$mxt0= ($z >>5)&0x07ffffff;

$mxt1= ($ii >>5)&0x07ffffff;

echo 0-1 : ".$mxt0."=".$mxt1;

}

 

And I get this output :    0-1 : 67108863=127231259

 

Can anyone give me a clue of what is going on???????

Please, need help

[boo_lolly]

maybe the manual will be of some help

http://www.php.net/manual/en/language.operators.bitwise.php

[utexas_pjm]

This code works for me:

 

<?php
$z = 4071400299;
$ii= 4071400299;
if ($ii==$z){
   $mxt0= ($z >>5)&0x07ffffff;
   $mxt1= ($ii >>5)&0x07ffffff;
   echo "0-1 : " .$mxt0."=".$mxt1;
}
?>

 

It is not possible for the values of $mxt0 and $mxt1 to be different provided that $z and $ii are equal.  Maybe you could post more code?

 

Patrick

[gorros]

I know it shouldn't happen, but it does!!!!!

 

Here are some more of my code, and input values

 

$ciptxt="-2982644431.4071400299.2046465665.-1438448000.1276185794";

$key="570526-1039";

 

function x($ciptxt,$key){

 

$v=explode(".",$ciptxt);

$k = str2long($key,false);

if (count($k) < 4)

for ($i = count($k); $i < 4; $i++)$k[$i] = 0;

 

$n = count($v);

$z = $v[$n-1];

$y = $v[0];

$delta = 0x9E3779B9;

$mx=0;

$e=0;

$q = 3;

$sum= $q*$delta;

 

$ii= 4071400299;

 

 

while ($sum!=0){

$e = $sum>>2 & 3;

for ($p = $n-1; $p > 0; $p--){

$z = $v[$p-1];

if ($ii==$z){

$mxt0= ($z >>5)&0x07ffffff;

$mxt1= ($ii >>5)&0x07ffffff;

echo "0-1 : ".$mxt0."=".$mxt1;

}else

$mxt1= ($v[$p-1] >>5)&0x07ffffff;

 

$mx = (($z >>5)&0x07ffffff^$y<<2) + (($y >>3)&0x1fffffff^$z<<4) ^ ($sum^$y) + ($k[$p&3^$e]^$z);

$v[$p] -= $mx;

$y = $v[$p];

}

$z = $v[$n-1];

$mx = (($z >>5)&0x07ffffff^$y<<2) + (($y >>3)&0x1fffffff^$z<<4) ^ ($sum^$y) + ($k[$p&3^$e]^$z);

$v[0] -= $mx;

$y=$v[0];

$sum -= $delta;

}

[utexas_pjm]

Try printing the values of $ii and $z inside the if statement.

[gorros]

If I make an echo of both parameters, they are the same

[gorros]

Here is the my str2long function. Try it and see what you get

 

 

function str2long($s, $w){

$v = unpack("V*", $s. str_repeat("\0", (4 - strlen($s) % 4) & 3));

$v = array_values($v);

if ($w)

$v[count($v)] = strlen($s);

return $v;

}

[utexas_pjm]

hmmm... I don't really know what to say... If you're sure that $z and $ii are the equal then your code is analogous to:

 

<?php
$a = 1;
$b = 1;
$a = $a + 1;
$b = $b + 1;
?>

 

I've come across weirdness with the shift operator before (usually problems with 32 => 64 bit architecture) but It makes no sense at all that running the same SHIFT and AND would result in two different values.  Sorry, I couldn't help.

 

Patrick

[gorros]

Did you try it?

[utexas_pjm]

<?
echo '<pre>' . print_r (str2long("foo", "bar"), true) . '</pre>';
function str2long($s, $w){   
   $v = unpack("V*", $s. str_repeat("\0", (4 - strlen($s) % 4) & 3));
   $v = array_values($v);
   if ($w)
      $v[count($v)] = strlen($s);
   return $v;
}
?>

 

Array

(

    [0] => 7303014

    [1] => 3

)

[gorros]

Did you run the primary function (x), withmy parameters? If so, what did you get?

[utexas_pjm]

I got:

0-1 : 67108863=127231259

 

Hmm... let me play with it for a bit.

[gorros]

At least it's not me that's crazy

[utexas_pjm]

I don't have a cause yet, but I have a solution:

 

<?php
         if ($ii==$z){
            $z = 4071400299;
            $mxt0= ($z >>5)&0x07ffffff;
            $mxt1= ($ii >>5)&0x07ffffff;
            echo "0-1 : ".$mxt0."=".$mxt1;
         }
?>

 

or

 

<?php
         if ($ii==$z){
            $mxt1= ($ii >>5)&0x07ffffff;
            $mxt0 = $mxt1;
            echo "0-1 : ".$mxt0."=".$mxt1;
         }
?>

 

For some reason the variable $z doesn't react well to the logical shift right.  By assigning $z to the scalar 4071400299, which is tautologically equivalent to the original the orginal code, the SHIFT and AND work as expected.  I'm curious as to why this happening...

 

Best,

 

Patrick

[gorros]

Problem is, the array will never be the same, and this error occur at random (to me at least) position, regardles of value or array-order

[gorros]

Unfortunatly (?) it doesn't happen for every value, or always at array-position "x".

I just can't understand what it is

[utexas_pjm]

Problem is, the array will never be the same, and this error occur at random (to me at least) position, regardles of value or array-order

 

I don't see what the array has anything to do with the problem.  You will only run this code when $z == $ii and $ii is statically set to 4071400299;

[gorros]

Nonono. SOrry. The if statement I just put in to test where/why it was failing

[Barand]

Looks like its to do with 4071400299 exceeding the value of a signed int

 

<?php
$x = 4071400299;
echo $x / 32, '<br>';
echo $x>>5, '<br><br>';

$x = 2071400299;
echo $x / 32, '<br>';
echo $x>>5;

?> 

[gorros]

No, it happen with any value.

But, I found a way to make it work.

 

After assigning the value, I make a call to settype($z,"double");

 

Maybe I should have known it, but it seem that this "auto" type assignement is a so-so

Anyway, thank's a lot for making me think in different ways

[btherl]

As an aside, the === operator will check both value and type.  Using that instead of == will show you when there are typing differences.  There's also a corresponding !== operator.

 

I use === by default, unless I am absolutely sure I want == for a specific case.