How is it quadratic? You do 1000 checks every character in the haystack but that's still O(n)

The worst case is that `std.mem.eql`[1] is executed at every position in the haystack, which gives you `O(n*m)` time complexity. Several substring search algorithms are `O(n)`.

[1]: https://github.com/aarol/substr/blob/9392f9557de735929dfb79e...