Fix variable names and comments in RandGenerator.

(No semantic change intended).

BUG=None
TEST=None


Review URL: http://codereview.chromium.org/7685053

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@98098 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 15 insertions, 17 deletions

diff --git a/base/rand_util.cc b/base/rand_util.cc
index e556c07..fcbccef 100644
--- a/base/rand_util.cc
+++ b/base/rand_util.cc
@@ -43,22 +43,21 @@ double BitsToOpenEndedUnitInterval(uint64 bits) {
   return result;
 }
 
-uint64 RandGenerator(uint64 max) {
-  DCHECK_GT(max, 0ULL);
-
+uint64 RandGenerator(uint64 range) {
+  DCHECK_GT(range, 0u);
   // We must discard random results above this number, as they would
   // make the random generator non-uniform (consider e.g. if
-  // MAX_UINT64 was 4 and max was 3, then a result of 1 would be twice
-  // as likely as a result of 0 or 2).
+  // MAX_UINT64 was 7 and |range| was 5, then a result of 1 would be twice
+  // as likely as a result of 3 or 4).
   uint64 max_acceptable_value =
-      (std::numeric_limits<uint64>::max() / max) * max;
+      (std::numeric_limits<uint64>::max() / range) * range - 1;
 
   uint64 value;
   do {
     value = base::RandUint64();
-  } while (value >= max_acceptable_value);
+  } while (value > max_acceptable_value);
 
-  return value % max;
+  return value % range;
 }
 
 void RandBytes(void* output, size_t output_length) {
diff --git a/base/rand_util.h b/base/rand_util.h
index c98cb45..4474c02 100644
--- a/base/rand_util.h
+++ b/base/rand_util.h
@@ -19,12 +19,12 @@ BASE_EXPORT uint64 RandUint64();
 // Returns a random number between min and max (inclusive). Thread-safe.
 BASE_EXPORT int RandInt(int min, int max);
 
-// Returns a random number in range [0, max).  Thread-safe.
+// Returns a random number in range [0, range).  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);
-BASE_EXPORT uint64 RandGenerator(uint64 max);
+BASE_EXPORT uint64 RandGenerator(uint64 range);
 
 // Returns a random double in range [0, 1). Thread-safe.
 BASE_EXPORT double RandDouble();
diff --git a/base/rand_util_unittest.cc b/base/rand_util_unittest.cc
index b81e2ef..a3474ba 100644
--- a/base/rand_util_unittest.cc
+++ b/base/rand_util_unittest.cc
@@ -4,6 +4,7 @@
 
 #include "base/rand_util.h"
 
+#include <algorithm>
 #include <limits>
 
 #include "testing/gtest/include/gtest/gtest.h"
@@ -29,16 +30,14 @@ TEST(RandUtilTest, RandDouble) {
 }
 
 TEST(RandUtilTest, RandBytes) {
-  const size_t buffer_size = 145;
+  const size_t buffer_size = 50;
   char buffer[buffer_size];
   memset(buffer, 0, buffer_size);
   base::RandBytes(buffer, buffer_size);
-  char accumulator = 0;
-  for(size_t i = 0; i < buffer_size; ++i)
-    accumulator |= buffer[i];
-  // In theory this test can fail, but it won't before the universe dies of
-  // heat death.
-  EXPECT_NE(0, accumulator);
+  std::sort(buffer, buffer + buffer_size);
+  // Probability of occurrence of less than 25 unique bytes in 50 random bytes
+  // is below 10^-25.
+  EXPECT_GT(std::unique(buffer, buffer + buffer_size) - buffer, 25);
 }
 
 TEST(RandUtilTest, RandBytesAsString) {