chrome/browser/metrics/perf/random_selector.cc

   1 // Copyright 2015 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "chrome/browser/metrics/perf/random_selector.h"
   6
   7 #include "base/logging.h"
   8 #include "base/rand_util.h"
   9 #include "base/strings/string_number_conversions.h"
  10 #include "base/strings/string_split.h"
  11 #include "base/strings/string_util.h"
  12
  13 RandomSelector::RandomSelector() : sum_of_weights_(0) {}
  14
  15 RandomSelector::~RandomSelector() {}
  16
  17 double RandomSelector::SumWeights(const std::vector<WeightAndValue>& odds) {
  18   double sum = 0.0;
  19   for (const auto& odd : odds) {
  20     sum += odd.weight;
  21   }
  22   return sum;
  23 }
  24
  25 void RandomSelector::SetOdds(const std::vector<WeightAndValue>& odds) {
  26   odds_ = odds;
  27   sum_of_weights_ = SumWeights(odds_);
  28 }
  29
  30 const std::string& RandomSelector::Select() {
  31   // Get a random double between 0 and the sum.
  32   double random = RandDoubleUpTo(sum_of_weights_);
  33   // Figure out what it belongs to.
  34   return GetValueFor(random);
  35 }
  36
  37 double RandomSelector::RandDoubleUpTo(double max) {
  38   CHECK_GT(max, 0.0);
  39   return max * base::RandDouble();
  40 }
  41
  42 const std::string& RandomSelector::GetValueFor(double random) {
  43   double current = 0.0;
  44   for (const auto& odd : odds_) {
  45     current += odd.weight;
  46     if (random < current)
  47       return odd.value;
  48   }
  49   NOTREACHED() << "Invalid value for key: " << random;
  50   return base::EmptyString();
  51 }