hex.ml

exception Error

let decode hex =
	let length = String.length hex in
	let div = length / 2 in
	let rem = length mod 2 in

	if rem != 0
	then raise Error
	;

	let string = String.create div in
	
	let to_int char =
		match char with
		| '0' -> 0
		| '1' -> 1
		| '2' -> 2
		| '3' -> 3
		| '4' -> 4
		| '5' -> 5
		| '6' -> 6
		| '7' -> 7
		| '8' -> 8
		| '9' -> 9
		| 'a' -> 10
		| 'b' -> 11
		| 'c' -> 12
		| 'd' -> 13
		| 'e' -> 14
		| 'f' -> 15
		| _ -> raise Error
	in

	let rec loop index length =
		if length != 0
		then begin
			let a = hex.[index * 2] in
			let b = hex.[index * 2 + 1] in
			let a' = to_int a in
			let b' = to_int b in
			let code = a' * 16 + b' in
			let char = Char.chr code in
			string.[index] <- char;
			loop (index + 1) (length - 1)
		end
	in		
	loop 0 div;
	string

let encode binary =
	let length = String.length binary in
	let mul = length * 2 in
	let string = String.create mul in
	
	let to_char int =
		match int with
		| 0 -> '0'
		| 1 -> '1'
		| 2 -> '2'
		| 3 -> '3'
		| 4 -> '4'
		| 5 -> '5'
		| 6 -> '6'
		| 7 -> '7'
		| 8 -> '8'
		| 9 -> '9'
		| 10 -> 'a'
		| 11 -> 'b'
		| 12 -> 'c'
		| 13 -> 'd'
		| 14 -> 'e'
		| 15 -> 'f'
		| _ -> raise Error
	in
	
	let rec loop index length =
		if length != 0
		then begin
			let char = binary.[index] in
			let code = Char.code char in
			let a = code / 16 in
			let b = code mod 16 in
			string.[index * 2] <- (to_char a);
			string.[index * 2 + 1] <- (to_char b);
			loop (index + 1) (length - 1)
		end
	in	
	loop 0 length;
	string