Add RandomNumberGenerator adapter to base/rand_util.h

BUG=46679
TEST=none (yet...)

Review URL: http://codereview.chromium.org/3053050

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@57904 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 24 insertions, 5 deletions

diff --git a/base/rand_util.cc b/base/rand_util.cc
index 8480c82..0576c94 100644
--- a/base/rand_util.cc
+++ b/base/rand_util.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2008 The Chromium Authors. All rights reserved.
+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -16,9 +16,8 @@ namespace base {
 int RandInt(int min, int max) {
   DCHECK(min <= max);
 
-  uint64 range = static_cast<int64>(max) - min + 1;
-  uint64 number = base::RandUint64();
-  int result = min + static_cast<int>(number % range);
+  uint64 range = static_cast<uint64>(max) - min + 1;
+  int result = min + static_cast<int>(base::RandGenerator(range));
   DCHECK(result >= min && result <= max);
   return result;
 }
@@ -37,4 +36,9 @@ double RandDouble() {
   return result;
 }
 
+uint64 RandGenerator(uint64 max) {
+  DCHECK(max > 0);
+  return base::RandUint64() % max;
+}
+
 }  // namespace base
diff --git a/base/rand_util.h b/base/rand_util.h
index 451a7d1..699fc7f 100644
--- a/base/rand_util.h
+++ b/base/rand_util.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2008 The Chromium Authors. All rights reserved.
+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -16,6 +16,13 @@ uint64 RandUint64();
 // Returns a random number between min and max (inclusive). Thread-safe.
 int RandInt(int min, int max);
 
+// Returns a random number in range [0, max).  Thread-safe.
+//
+// Note that this can be used as an adapter for std::random_shuffle():
+// Given a pre-populated |std::vector<int> myvector|, shuffle it as
+//   std::random_shuffle(myvector.begin(), myvector.end(), base::RandGenerator);
+uint64 RandGenerator(uint64 max);
+
 // Returns a random double in range [0, 1). Thread-safe.
 double RandDouble();
 
diff --git a/base/rand_util_unittest.cc b/base/rand_util_unittest.cc
index f56c0ec..cbc338a 100644
--- a/base/rand_util_unittest.cc
+++ b/base/rand_util_unittest.cc
@@ -27,3 +27,11 @@ TEST(RandUtilTest, RandDouble) {
  EXPECT_GT(1.0, number);
  EXPECT_LE(0.0, number);
 }
+
+// Make sure that it is still appropriate to use RandGenerator in conjunction
+// with std::random_shuffle().
+TEST(RandUtilTest, RandGeneratorForRandomShuffle) {
+  EXPECT_EQ(base::RandGenerator(1), 0U);
+  EXPECT_LE(std::numeric_limits<ptrdiff_t>::max(),
+            std::numeric_limits<int64>::max());
+}