Constructs a new phpass password hashing instance.
int $countLog2: Password stretching iteration count. Specifies the number of times the hashing function will be applied when generating new password hashes. The number of times is calculated by raising 2 to the power of the given value.
function __construct($countLog2) {
// Ensure that $countLog2 is within set bounds.
$this->countLog2 = $this
->enforceLog2Boundaries($countLog2);
}