sub ikegami_exp { my ($x) = @_; my $last = 0; my $result = 1; my $acc = 1; for (my $n = 1; abs($result-$last)>0; $n++) { $last = $result; $acc *= $x/$n; $result += $acc; } return $result; } for (1, 0.1, 10, 3.14, 0.1234, 100) { printf("%.16e: exp() = %.16e ikegami_exp() = %.16e\n", $_, exp($_), ikegami_exp($_), ); }