entropy overlap testing

chrome/common/metrics/entropy_provider_unittest.cc

 // Copyright (c) 2012 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.
 
 #include <cmath>
 #include <limits>
 #include <numeric>
 
 #include "base/basictypes.h"
 #include "base/guid.h"
@@ skipping 317 matching lines @@
 
       ++count;
     }
 
     ASSERT_LT(count, kMaxAttempts) << "Expected average was " <<
         kExpectedAverage << ", average ended at " << cumulative_average <<
         ", for trial " << kTestTrialNames[i];
   }
 }
 
+TEST_F(EntropyProviderTest, Overlap) {
+  const std::string kTrial1Name = "UMA-Uniformity-Trial-5-Percent";
+  const int kTrial1GroupCount = 20;
+  std::vector<uint16> trial_1_mapping(kMaxLowEntropySize);
+  internal::PermuteMappingUsingTrialName(kTrial1Name, &trial_1_mapping);
+
+  const std::string kTrial2Name = "UMA-Uniformity-Trial-10-Percent";
+  const int kTrial2GroupCount = 10;
+  std::vector<uint16> trial_2_mapping(kMaxLowEntropySize);
+  internal::PermuteMappingUsingTrialName(kTrial2Name, &trial_2_mapping);
+
+  const double kEntropyDivisor = static_cast<double>(kMaxLowEntropySize);
+
+  std::vector<std::vector<int> > counts; // trial1,trial2
+  counts.resize(kTrial1GroupCount);
+  for (size_t i = 0; i < kTrial1GroupCount; ++i)
+    counts[i].resize(kTrial2GroupCount);
+
+  for (size_t i = 0; i < kMaxLowEntropySize; ++i) {
+    uint16 trial_1_mapped_entropy = trial_1_mapping[i];
+    double trial_1_random_value = trial_1_mapped_entropy / kEntropyDivisor;
+    int trial_1_group = trial_1_random_value * kTrial1GroupCount;
+
+    uint16 trial_2_mapped_entropy = trial_2_mapping[i];
+    double trial_2_random_value = trial_2_mapped_entropy / kEntropyDivisor;
+    int trial_2_group = trial_2_random_value * kTrial2GroupCount;
+
+    counts[trial_1_group][trial_2_group]++;
+  }
+
+  for (size_t i = 0; i < counts.size(); ++i) {
+    for (size_t j = 0; j < counts[i].size(); j++) {
+      printf("%d\t", counts[i][j]);
+    }
+    puts("");
+  }
+}
+
 }  // namespace metrics