add sha512-224sum (SHA512/224) and sha512-256sum (SHA512/256)

Signed-off-by: Mattias Andrée <maandree@kth.se>

sha512-256.h

@@ -0,0 +1,16 @@
+/* public domain sha512/256 implementation based on fips180-3 */
+
+#include "sha512.h"
+
+#define sha512_256  sha512  /*struct*/
+
+enum { SHA512_256_DIGEST_LENGTH = 32 };
+
+/* reset state */
+void sha512_256_init(void *ctx);
+/* process message */
+#define sha512_256_update  sha512_update
+/* get message digest */
+/* state is ruined after sum, keep a copy if multiple sum is needed */
+/* part of the message might be left in s, zero it if secrecy is needed */
+void sha512_256_sum(void *ctx, uint8_t md[SHA512_256_DIGEST_LENGTH]);