// probe/exp-test.cc
  
  // Copyright 2014  Yandex LLC (Author: Ilya Edrenkin)
  
  // See ../../COPYING for clarification regarding multiple authors
  //
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  //
  //  http://www.apache.org/licenses/LICENSE-2.0
  //
  // THIS CODE IS PROVIDED *AS IS* BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  // KIND, EITHER EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION ANY IMPLIED
  // WARRANTIES OR CONDITIONS OF TITLE, FITNESS FOR A PARTICULAR PURPOSE,
  // MERCHANTABLITY OR NON-INFRINGEMENT.
  // See the Apache 2 License for the specific language governing permissions and
  // limitations under the License.
  
  // Read Makefile.slow_expf. This test must be compiled with -O0.
  
  #include <iostream>
  #include <cmath>
  #include "base/timer.h"
  
  int main() {
    int test_iter = 300000;
  
    // Make sure that the CPU bumps its clock to full speed: run the first loop
    // without timing. Then increase the sample iteration count exponentially
    // until the loop takes at least 10ms. We run this loop 1/4 of the number of
    // actual test iterations and call both exp() and expf(), so that the overall
    // test run will take 20 to 60 ms, to ensure a sensibly measurable result.
    for (bool first = true; ; first=false) {
      kaldi::Timer timer;
      for(int i = 0; i < test_iter; i += 4) {
        (void)exp((double)(i & 0x0F));
        (void)expf((double)(i & 0x0F));
      }
      double time = timer.Elapsed();
      if (first) continue;
      if (time > 0.01) break;
      test_iter *= 3;
    }
  
    kaldi::Timer exp_timer;
    for(int i = 0; i < test_iter; ++i) {
      (void)exp((double)(i & 0x0F));
    }
    double exp_time = exp_timer.Elapsed();
  
    kaldi::Timer expf_timer;
    for(int i = 0; i < test_iter; ++i) {
      (void)expf((double)(i & 0x0F));
    }
    double expf_time = expf_timer.Elapsed();
  
    double ratio = expf_time / exp_time;
    if (ratio < 1.1) {
      // Often exp() and expf() perform very similarly, so we will replace expf()
      // by exp() only if there is at least 10% difference.
      return 0;
    }
  
    std::cerr << ("WARNING: slow expf() detected. expf() is slower than exp() "
                  "by the factor of ") << ratio << "
  ";
    return 1;
  }