A simply memoised recursive fib will outstrip most iterative methods: 

sub fib_memo {
    state $memo = { 1 => 1, 2 => 1 };
    return $memo->{ $_[0] } //= fib_memo( $_[0] - 1 ) + fib_memo( $_[0
+] - 2 );
}

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In reply to Re^2: fibonacci numbers using subroutine? by BrowserUk
in thread fibonacci numbers using subroutine? by derpp

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