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

base/rand_util_posix.cc

Index: base/rand_util_posix.cc
diff --git a/base/rand_util_posix.cc b/base/rand_util_posix.cc
index 082d64923d5b9bf63890565bcf922eb361cc3ab3..7a10ffd89f2d3b67a678abe416d50369c0d6b708 100644
--- a/base/rand_util_posix.cc
+++ b/base/rand_util_posix.cc
@@ -20,19 +20,16 @@ namespace {
 // we can use LazyInstance to handle opening it on the first access.
 class URandomFd {
  public:
-  URandomFd() {
-    fd_ = open("/dev/urandom", O_RDONLY);
+  URandomFd() : fd_(open("/dev/urandom", O_RDONLY)) {
     DCHECK_GE(fd_, 0) << "Cannot open /dev/urandom: " << errno;
   }
 
-  ~URandomFd() {
-    close(fd_);
-  }
+  ~URandomFd() { close(fd_); }
 
   int fd() const { return fd_; }
 
  private:
-  int fd_;
+  const int fd_;
 };
 
 base::LazyInstance<URandomFd>::Leaky g_urandom_fd = LAZY_INSTANCE_INITIALIZER;
@@ -42,14 +39,16 @@ base::LazyInstance<URandomFd>::Leaky g_urandom_fd = LAZY_INSTANCE_INITIALIZER;
 namespace base {
 
 // NOTE: This function must be cryptographically secure. http://crbug.com/140076

[wtc, 2014/01/22 22:29:09]

This comment should be in front of RandUint64(). I think this comment doesn't
make sense, but you should avoid dealing with this issue in this CL.

[DaleCurtis, 2014/01/22 22:54:14]

Done.

-uint64 RandUint64() {
-  uint64 number;
-
-  int urandom_fd = g_urandom_fd.Pointer()->fd();
-  bool success = ReadFromFD(urandom_fd, reinterpret_cast<char*>(&number),
-                            sizeof(number));
+void RandBytes(void* output, size_t output_length) {

[wtc, 2014/01/22 22:29:09]

Define RandBytes after RandUint64, as the Style Guide recommends.

[DaleCurtis, 2014/01/22 22:54:14]

Done.

+  const int urandom_fd = g_urandom_fd.Pointer()->fd();
+  const bool success =
+      ReadFromFD(urandom_fd, static_cast<char*>(output), output_length);
   CHECK(success);
+}
 
+uint64 RandUint64() {
+  uint64 number;
+  RandBytes(&number, sizeof(number));
   return number;
 }