Decrypted code level 1:

$_F=__FILE__;
$_X='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';
$_X=base64_decode($_X);
$_X=strtr($_X,'123456aouie','aouie123456');
$_X=str_ireplace ('function_','function',$_X);
$_R=preg_replace('/__FILE__/',"'".$_F."'",$_X);
eval($_R);
$_R=0;
$_X=0;

Decrypted code level 2:

$_F='/var/www/malwaredecoder/application/models/Decoder_model.php(664) : eval()'d code';
$_X='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';
eval(base64_decode('JF9YPWJhc2U2NF9kZWNvZGUoJF9YKTskX1g9c3RydHIoJF9YLCcxMjM0NTZhb3VpZScsJ2FvdWllMTIzNDU2Jyk7JF9YPXN0cl9pcmVwbGFjZSAoJ2Z1bmN0aW9uXycsJ2Z1bmN0aW9uJywkX1gpOyRfUj1wcmVnX3JlcGxhY2UoJy9fX0ZJTEVfXy8nLCInIi4kX0YuIiciLCRfWCk7ZXZhbCgkX1IpOyRfUj0wOyRfWD0wOw=='));

Decrypted code level 3:

$_F='/var/www/malwaredecoder/application/models/Decoder_model.php(664) : echo )'d code';
$_X='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';
eval(base64_decode('JF9YPWJhc2U2NF9kZWNvZGUoJF9YKTskX1g9c3RydHIoJF9YLCcxMjM0NTZhb3VpZScsJ2FvdWllMTIzNDU2Jyk7JF9YPXN0cl9pcmVwbGFjZSAoJ2Z1bmN0aW9uXycsJ2Z1bmN0aW9uJywkX1gpOyRfUj1wcmVnX3JlcGxhY2UoJy9fX0ZJTEVfXy8nLCInIi4kX0YuIiciLCRfWCk7ZXZhbCgkX1IpOyRfUj0wOyRfWD0wOw==');

$_F='/var/www/malwaredecoder/application/models/Decoder_model.php(664) : echo )'d code';
$_X='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';
echo base64_decode('JF9YPWJhc2U2NF9kZWNvZGUoJF9YKTskX1g9c3RydHIoJF9YLCcxMjM0NTZhb3VpZScsJ2FvdWllMTIzNDU2Jyk7JF9YPXN0cl9pcmVwbGFjZSAoJ2Z1bmN0aW9uXycsJ2Z1bmN0aW9uJywkX1gpOyRfUj1wcmVnX3JlcGxhY2UoJy9fX0ZJTEVfXy8nLCInIi4kX0YuIiciLCRfWCk7ZXZhbCgkX1IpOyRfUj0wOyRfWD0wOw==';