+ RC4 is a stream cipher. We're not using it here for its
+ cryptographic properties, but because it is easy to implement
+ and its output is plenty random for non-cryptographic
+ purposes.
+
+ See http://en.wikipedia.org/wiki/RC4_(cipher) for information
+ on RC4.*/
+
+/* RC4 state. */
+static uint8_t s[256]; /* S[]. */
+static uint8_t s_i, s_j; /* i, j. */
+
+/* Already initialized? */
+static bool inited;
+
+/* Swaps the bytes pointed to by A and B. */