(* your code goes here *)(* hex to raw bytes *)
let rec hex_to_raw hexstring = 
  let rec hexraw hexstr rawstr = 
    let tophex = String.sub hexstr 0 2 in
    let topint = int_of_string ("0x" ^ tophex) in
    let newrawstr = rawstr ^ (String.make 1 (Char.chr topint)) in
    let remlen = (String.length hexstr) - 2  in
    if remlen = 0 then newrawstr
    else hexraw (String.sub hexstr 2 remlen) newrawstr in
  hexraw hexstring "" ;;
 
let b64_to_raw b64string =
  b64string ;;
 
let raw_to_hex rawstring =
  rawstring ;;
 
let raw_to_b64 rawstring =
  rawstring ;;
 
Printf.printf "%s" (raw_to_b64 (hex_to_raw "badf00d"))

KCogeW91ciBjb2RlIGdvZXMgaGVyZSAqKSgqIGhleCB0byByYXcgYnl0ZXMgKikKbGV0IHJlYyBoZXhfdG9fcmF3IGhleHN0cmluZyA9IAogIGxldCByZWMgaGV4cmF3IGhleHN0ciByYXdzdHIgPSAKICAgIGxldCB0b3BoZXggPSBTdHJpbmcuc3ViIGhleHN0ciAwIDIgaW4KICAgIGxldCB0b3BpbnQgPSBpbnRfb2Zfc3RyaW5nICgiMHgiIF4gdG9waGV4KSBpbgogICAgbGV0IG5ld3Jhd3N0ciA9IHJhd3N0ciBeIChTdHJpbmcubWFrZSAxIChDaGFyLmNociB0b3BpbnQpKSBpbgogICAgbGV0IHJlbWxlbiA9IChTdHJpbmcubGVuZ3RoIGhleHN0cikgLSAyICBpbgogICAgaWYgcmVtbGVuID0gMCB0aGVuIG5ld3Jhd3N0cgogICAgZWxzZSBoZXhyYXcgKFN0cmluZy5zdWIgaGV4c3RyIDIgcmVtbGVuKSBuZXdyYXdzdHIgaW4KICBoZXhyYXcgaGV4c3RyaW5nICIiIDs7CgpsZXQgYjY0X3RvX3JhdyBiNjRzdHJpbmcgPQogIGI2NHN0cmluZyA7OwoKbGV0IHJhd190b19oZXggcmF3c3RyaW5nID0KICByYXdzdHJpbmcgOzsKCmxldCByYXdfdG9fYjY0IHJhd3N0cmluZyA9CiAgcmF3c3RyaW5nIDs7CgpQcmludGYucHJpbnRmICIlcyIgKHJhd190b19iNjQgKGhleF90b19yYXcgImJhZGYwMGQiKSk=