Added SHAKE128/256 code and test vectors.

sha3.h

@@ -7,8 +7,8 @@
 #include <stddef.h>
 #include <stdint.h>
 
-#ifndef SHA3_ROUNDS
-#define SHA3_ROUNDS 24
+#ifndef KECCAKF_ROUNDS
+#define KECCAKF_ROUNDS 24
 #endif
 
 #ifndef ROTL64
@@ -32,5 +32,13 @@ int sha3_final(void *md, sha3_ctx_t *c);    // digest goes to md
 // compute a sha3 hash (md) of given byte length from "in"
 void *sha3(const void *in, size_t inlen, void *md, int mdlen);
 
+// SHAKE128 and SHAKE256 extensible-output functions
+#define shake128_init(c) sha3_init(c, 16)
+#define shake256_init(c) sha3_init(c, 32)
+#define shake_update sha3_update
+
+void shake_xof(sha3_ctx_t *c);
+void shake_out(sha3_ctx_t *c, void *out, size_t len);
+
 #endif