cryptography - Feistel Cipher in c# -

i'm trying implement feistel cipher, have following code:

public static byte[] encode(byte[] bytes) {         byte[] s = (byte[])bytes.clone();         int half = s.length / 2;         if (s.length % 2 != 0)             throw new exception("unbalanced code");         byte[] left = new byte[half];         byte[] right = new byte[half];         array.copy(s, left, half);         array.copy(s, half, right, 0, half);          (var k = 0; k < rounds; k++) {             left = xor(left,f(right));             var temp = left; left = right; right = temp;         }           byte[] toreturn = new byte[s.length];         array.copy(left, 0, toreturn, half, half);         array.copy(right, 0, toreturn, 0, half);          return toreturn;     } 

in sample, rounds 21 , f function rearranges bytes in array of bytes.

unfortunately, while bytes should equal encode(encode(bytes)), it's not. , have no idea i'm doing wrong.

any advice?

edit: code f()

public static byte[] f(byte[] s) {         byte[] toreturn = (byte[])s.clone();         byte temp = s[0];         (var k = 1; k < s.length; k++) {             s[k-1] = s[k];             s[k - 1] = (byte)(s[k - 1] ^ 45);         }         s[s.length - 1] = temp;         s[s.length - 1] = (byte)(s[s.length - 1] ^ 45);         return toreturn;     } 

codesinchaos correct, problem variable being mutated.