SSE optimized Salsa20 -- anywhere from 20% to 50% faster than plain C version

node/Salsa20.hpp

@@ -11,6 +11,17 @@
 
 #include "Constants.hpp"
 
+#ifdef ZT_SALSA20_SSE
+#include <emmintrin.h>
+#ifdef __GCC__
+#define ZT_SALSA20_SSE_ALIGN __attribute__((aligned (16)))
+#else
+#define ZT_SALSA20_SSE_ALIGN __declspec(align(16))
+#endif
+#else
+#define ZT_SALSA20_SSE_ALIGN
+#endif
+
 namespace ZeroTier {
 
 /**
@@ -68,7 +79,12 @@ public:
 	}
 
 private:
-	uint32_t _state[16];
+	volatile ZT_SALSA20_SSE_ALIGN union {
+#ifdef ZT_SALSA20_SSE
+		__m128i v[4];
+#endif
+		uint32_t i[16];
+	} _state;
 	unsigned int _roundsDiv2;
 };