add blake2b writer

src/hash.h

@@ -12,6 +12,8 @@
 #include "uint256.h"
 #include "version.h"
 
+#include "sodium.h"
+
 #include <vector>
 
 typedef uint256 ChainCode;
@@ -150,6 +152,47 @@ public:
     }
 };
 
+
+/** A writer stream (for serialization) that computes a 256-bit BLAKE2b hash. */
+class CBLAKE2bWriter
+{
+private:
+    crypto_generichash_blake2b_state state;
+
+public:
+    int nType;
+    int nVersion;
+
+    CBLAKE2bWriter(int nTypeIn, int nVersionIn, const unsigned char* personal) : nType(nTypeIn), nVersion(nVersionIn) {
+        assert(crypto_generichash_blake2b_init_salt_personal(
+            &state,
+            NULL, 0, // No key.
+            32,
+            NULL,    // No salt.
+            personal) == 0);
+    }
+
+    CBLAKE2bWriter& write(const char *pch, size_t size) {
+        crypto_generichash_blake2b_update(&state, (const unsigned char*)pch, size);
+        return (*this);
+    }
+
+    // invalidates the object
+    uint256 GetHash() {
+        uint256 result;
+        crypto_generichash_blake2b_final(&state, (unsigned char*)&result, 32);
+        return result;
+    }
+
+    template<typename T>
+    CBLAKE2bWriter& operator<<(const T& obj) {
+        // Serialize to this stream
+        ::Serialize(*this, obj, nType, nVersion);
+        return (*this);
+    }
+};
+
+
 /** Compute the 256-bit hash of an object's serialization. */
 template<typename T>
 uint256 SerializeHash(const T& obj, int nType=SER_GETHASH, int nVersion=PROTOCOL_VERSION)