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signed / unsigned integer problem

Posted on 2003-10-25
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Last Modified: 2008-02-01
I have a function in C++:

    int gg_login_hash(char *password, int seed) {
            unsigned int x, y, z;

            y = seed;

            for (x = 0; *password; password++) {
                    x = (x & 0xffffff00) | *password;
                    y ^= x;
                    y += x;
                    x <<= 8;
                    y ^= x;
                    x <<= 8;
                    y -= x;
                    x <<= 8;
                    y ^= x;

                    z = y & 0x1f;
                    y = (y << z) | (y >> (32 - z));
          }
          return y;
    }
   
... and i have converted it to PHP:

    function ggLoginHash($password, $seed) {
   
        $y = $seed;
        $x = 0;
        for ($nr = 0, $length = strlen($password); $nr < $length; $nr++) {
            $x = ($x & 0xFFFFFF00) | ord($password[$nr]);
            $y ^= $x;
            $y += $x;
            $x <<= 8;
            $y ^= $x;
            $x <<= 8;
            $y -= $x;
            $x <<= 8;
            $y ^= $x;
           
            $z = $y & 0x1F;
            $y = ($y << $z) | ($y >> (32 - $z));
        }
        return $y;
    }

The problem is that it doesn't realy seem to return the same value.
I think the problem is that there are variables in the C++ code marked as unsigned int, which i can not do in PHP.
Can someone help me converting that so it will work correctly?

Example:
Calling code from C++:
gg_login_hash("dupa", 128) gives 1453413288 in a result.
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Question by:Lukasz Lach
1 Comment
 
LVL 14

Accepted Solution

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ThG earned 125 total points
ID: 9621561

Hmm, /me thinks.
From a quick debug looks like the $y >> (32 - $z) is performing an aritmetic shift right rather than a logical shift right, as it does (and should do) in C.
This made me think a little so i decided to check the PHP manual for the bitwise operators and in fact a comment points out that all the shift operations are signed (thus aritmetical). Very bad!

So here is a hackish workaround to clean the sign and complete the shifting:
 ...
            $z = $y & 0x1F;
            $y1 = ($y << $z);
            $y2 = 0;
            if ($z < 32) {
              $y2 = $y >> 1;
              $y2 &= 0x7fffffff;
              $y2 = $y2 >> (31 - $z);
            }
            $y = $y1 | $y2;
 ...

I'm the best PHP coder ;-)
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