Avoids MSVC warnings about possible value truncation.

nss/lib/freebl/chacha20/chacha20.c

Index: nss/lib/freebl/chacha20/chacha20.c
diff --git a/nss/lib/freebl/chacha20/chacha20.c b/nss/lib/freebl/chacha20/chacha20.c
index 34bea804e7d8cad5cc12b7e53055a5fb6c3fc46d..50b9aad6a8a94010bca4bb828c4fa57bba5b1571 100644
--- a/nss/lib/freebl/chacha20/chacha20.c
+++ b/nss/lib/freebl/chacha20/chacha20.c
@@ -78,7 +78,7 @@ void ChaCha20XOR(unsigned char *out, const unsigned char *in, unsigned int inLen
     input[2] = U8TO32_LITTLE(sigma + 8);
     input[3] = U8TO32_LITTLE(sigma + 12);
 
-    input[12] = counter;
+    input[12] = (PRUint32)counter;
     input[13] = counter >> 32;

[wtc, 2014/08/28 20:45:11]

Just wanted to confirm: this line doesn't require a PRUint32 cast, right?

[agl, 2014/08/28 20:51:30]

I might be tempted to put it anyway. I would guess that the compiler is figuring
out that |counter >> 32| is in-range because of the shift, but that seems like
quite a lot of intelligence.

[Peter Kasting, 2014/08/28 21:11:44]

MSVC doesn't require the cast to avoid triggering a warning here, because as agl
suspects, it understands that ">> n" means the top n bits don't matter and can
be safely truncated.

I have no opinion on whether you should add a cast anyway.  I'm not inserting
such casts in other CLs for other codebases I'm modifying as part of this
change.

     input[14] = U8TO32_LITTLE(nonce + 0);
     input[15] = U8TO32_LITTLE(nonce + 4);