1    :  // Copyright 2011 Google Inc. All Rights Reserved.
   2    :  //
   3    :  // Licensed under the Apache License, Version 2.0 (the "License");
   4    :  // you may not use this file except in compliance with the License.
   5    :  // You may obtain a copy of the License at
   6    :  //
   7    :  //     http://www.apache.org/licenses/LICENSE-2.0
   8    :  //
   9    :  // Unless required by applicable law or agreed to in writing, software
  10    :  // distributed under the License is distributed on an "AS IS" BASIS,
  11    :  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  12    :  // See the License for the specific language governing permissions and
  13    :  // limitations under the License.
  14    :  
  15    :  #include "syzygy/core/random_number_generator.h"
  16    :  #include "base/logging.h"
  17    :  
  18    :  // This is a linear congruent pseudo random generator.
  19    :  // See: http://en.wikipedia.org/wiki/Linear_congruential_generator.
  20    :  
  21    :  namespace {
  22    :  
  23    :  const int kA = 1103515245;
  24    :  const int kC = 12345;
  25    :  
  26    :  }  // namespace
  27    :  
  28    :  namespace core {
  29    :  
  30  E :  RandomNumberGenerator::RandomNumberGenerator(uint32 seed) : seed_(seed) {
  31  E :  }
  32    :  
  33  E :  uint32 RandomNumberGenerator::operator()(uint32 n) {
  34    :    // The generator is g(N + 1) = (g(N) * kA + kC) mod 2^32.
  35    :    // The use of unsigned 32 bit values yields the mod 2^32 for free.
  36  E :    seed_ = seed_ * kA + kC;
  37  E :    uint32 ret = seed_ % n;
  38  E :    DCHECK_GT(n, ret);
  39  E :    return ret;
  40  E :  }
  41    :  
  42    :  }  // namespace core