def subnet_count(prefix_len)
			if (prefix_len <= self.netmask.prefix_len || prefix_len > 32 || prefix_len - self.netmask.prefix_len >= 32)
				return 0
			end
			return 1 << (prefix_len - self.netmask.prefix_len)
		end
def subnet_count(prefix_len)
			if (prefix_len <= self.netmask.prefix_len || prefix_len > 32 || prefix_len - self.netmask.prefix_len >= 32)
				return 0
			end
			return 1 << (prefix_len - self.netmask.prefix_len)
		end
subnet_count returns the number a subnets of a given prefix length that this IPv4Net contains.
 It will return 0 for invalid requests (ie. bad prefix or prefix is shorter than that of this network).
 It will also return 0 if the result exceeds the capacity of a 32-bit integer (ie. if you want the # of /32 a /0 will hold)