csail/6006psets_ng — comment on commit 567e292441d2a5cf99f7e43da25f0907762876fa
File: 5/code/rsa/big_num.rb line 72
By pwnall:

`+=` is particularly slow, like in Python. You need `<<`, which is like `append`.

Alternatively, you can do `@d[0, start + 1].reverse!.map(&:to_hex).join`