Fix ChaCha NEON compile with MSVC compiler (GH #776)

chacha_simd.cpp

@@ -70,6 +70,15 @@ ANONYMOUS_NAMESPACE_BEGIN
 
 // ***************************** NEON ***************************** //
 
+// Thanks to Peter Cordes, https://stackoverflow.com/q/54016821/608639
+#if (CRYPTOPP_ARM_NEON_AVAILABLE)
+# if defined(_MSC_VER)
+#  define PACK32x4(w,x,y,z) { ((w) + (word64(x) << 32)), ((y) + (word64(z) << 32)) }
+# else
+#  define PACK32x4(w,x,y,z) { (w), (x), (y), (z) }
+# endif
+#endif  // Microsoft workaround
+
 #if (CRYPTOPP_ARM_NEON_AVAILABLE)
 
 template <unsigned int R>
@@ -303,7 +312,9 @@ void ChaCha_OperateKeystream_NEON(const word32 *state, const byte* input, byte *
     const uint32x4_t state3 = vld1q_u32(state + 3*4);
 
     const uint32x4_t CTRS[3] = {
-        {1,0,0,0}, {2,0,0,0}, {3,0,0,0}
+        PACK32x4(1,0,0,0),
+        PACK32x4(2,0,0,0),
+        PACK32x4(3,0,0,0)
     };
 
     uint32x4_t r0_0 = state0;