Avoids MSVC warnings about possible value truncation.

nss/lib/freebl/chacha20/chacha20.c

 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 /* Adopted from the public domain code in NaCl by djb. */
 
 #include <string.h>
 #include <stdio.h>
 
 #include "prtypes.h"
@@ skipping 60 matching lines @@
     input[8] = U8TO32_LITTLE(key + 16);
     input[9] = U8TO32_LITTLE(key + 20);
     input[10] = U8TO32_LITTLE(key + 24);
     input[11] = U8TO32_LITTLE(key + 28);
 
     input[0] = U8TO32_LITTLE(sigma + 0);
     input[1] = U8TO32_LITTLE(sigma + 4);
     input[2] = U8TO32_LITTLE(sigma + 8);
     input[3] = U8TO32_LITTLE(sigma + 12);
 
-    input[12] = counter;
-    input[13] = counter >> 32;
+    input[12] = (PRUint32)counter;
+    input[13] = (PRUint32)(counter >> 32);
     input[14] = U8TO32_LITTLE(nonce + 0);
     input[15] = U8TO32_LITTLE(nonce + 4);
 
     while (inLen >= 64) {
         ChaChaCore(block, input, 20);
         for (i = 0; i < 64; i++) {
             out[i] = in[i] ^ block[i];
         }
 
         input[12]++;
         if (input[12] == 0) {
             input[13]++;
         }
 
         inLen -= 64;
         in += 64;
         out += 64;
     }
 
     if (inLen > 0) {
         ChaChaCore(block, input, 20);
         for (i = 0; i < inLen; i++) {
             out[i] = in[i] ^ block[i];
         }
     }
 }