Improve base::RandBytes() performance by 1.75x-2.10x on POSIX.

base/rand_util_nacl.cc

Index: base/rand_util_nacl.cc
diff --git a/base/rand_util_nacl.cc b/base/rand_util_nacl.cc
index 47450aaba68be254001da2f5e9d84e182b19ed76..f9751217326b4c72730b98fa1018be49f12a4b1a 100644
--- a/base/rand_util_nacl.cc
+++ b/base/rand_util_nacl.cc
@@ -14,21 +14,21 @@ namespace {
 class NaclRandom {
  public:
   NaclRandom() {
-    size_t result = nacl_interface_query(NACL_IRT_RANDOM_v0_1,
-                                         &random_, sizeof(random_));
+    const size_t result =
+        nacl_interface_query(NACL_IRT_RANDOM_v0_1, &random_, sizeof(random_));
     CHECK_EQ(result, sizeof(random_));
   }
 
-  ~NaclRandom() {
-  }
+  ~NaclRandom() {}
 
-  void GetRandomBytes(char* buffer, uint32_t num_bytes) {
+  void GetRandomBytes(void* output, size_t num_bytes) {
+    char* output_ptr = static_cast<char*>(output);
     while (num_bytes > 0) {
       size_t nread;
-      int error = random_.get_random_bytes(buffer, num_bytes, &nread);
+      const int error = random_.get_random_bytes(output_ptr, num_bytes, &nread);
       CHECK_EQ(error, 0);
       CHECK_LE(nread, num_bytes);
-      buffer += nread;
+      output_ptr += nread;
       num_bytes -= nread;
     }
   }
@@ -43,11 +43,15 @@ base::LazyInstance<NaclRandom>::Leaky g_nacl_random = LAZY_INSTANCE_INITIALIZER;
 
 namespace base {
 
+// NOTE: This function must be cryptographically secure. http://crbug.com/140076
 uint64 RandUint64() {
   uint64 result;
-  g_nacl_random.Pointer()->GetRandomBytes(
-      reinterpret_cast<char*>(&result), sizeof(result));
+  g_nacl_random.Pointer()->GetRandomBytes(&result, sizeof(result));
   return result;
 }
 
+void RandBytes(void* output, size_t output_length) {
+  g_nacl_random.Pointer()->GetRandomBytes(output, output_length);
+}
+
 }  // namespace base