Decryption error when KSN serial is > 10

[avbdr]

Hello,
Im using your library to decrypt tracks of a Magtek Reader and for some reasons
Im able to decrypt tracks with ksn serial < 10 while rest are failing.
If ksn is 9014030B2ABDC0000005 then decryption works, when ksn is like 9014030B2ABDC0000050
im getting garbage in return.

I do not mind to pay for a consulting. Thank you.

   $key = new DUKPT\KeySerialNumber($ksn);
   $encryptionKey = DUKPT\DerivedKey::calculatePinEncryptionKey ($key, $bdkMagtek);

Thank you for a library.

[avbdr]

Ok. Seems I found a fix. but i do not understand this piece of code.
in calculateDerivedKey

-                  $r8 = Utility::orHexString($r8, $shiftr, 43);
+                 $r8 = Utility::orHexString($r8, $shiftr, 59);

Thats what i did to make decryption on Rambler reader to work. Magtek needed original padding of 43 to work properly.

From where this constant comes?