This isn't a fair criticism for the C implementation. The output doesn't even remotely fit in a 32-bit int, which is what this implementation is for. "Moderate

This isn't a fair criticism for the C implementation. The output doesn't even remotely fit in a 32-bit int, which is what this implementation is for. "Moderately sized inputs" is a misleading thing to say for a function that grows exponentially. Would you protest that the ones digit in exp(80) is wrong in double-precision IEEE 754 arithmetic? The formula isn't innacurate. It's simply using data types that can't fit everything. The point of the article is that Binet's formula is something that should at least be mentioned when presenting the classical introductory examples of recursion to programmers. It's unfair to praise simplistic recursive functions without even mentioning that the same result can be obtained in a much more mathematically elegant way.