ねえ
// int[] sKey
// byte[] wKey
// int data
wKey[0] += sKey[(int) wKey[1] & 0xFF] - data;
wKey[1] -= (byte) ((sKey[(int) data & 0xFF] ^ wKey[2]) & 0xFF);
wKey[2] ^= (byte) (data + sKey[(int) wKey[3] & 0xFF]) & 0xFF;
wKey[3] -= (byte) (wKey[0] - sKey[(int) data & 0xFF]) & 0xFF;

int dKey = ((int) wKey[0]) & 0xFF | (wKey[1] << 8) & 0xFF00 | (wKey[2] << 16) & 0xFF0000 | (wKey[3] << 24) & 0xFF000000;

こういうのってKotlinでどう書けばいいの…