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 *
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 * in the documentation and/or other materials provided with the
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 * this software without specific prior written permission.
 *
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#include "statsreport/common/highres_timer.h"

bool HighresTimer::perf_freq_collected_ = false;
ULONGLONG HighresTimer::perf_freq_ = 0;

ULONGLONG HighresTimer::GetElapsedMs() const {
  ULONGLONG end_time = GetCurrentTicks();

  // Scale to ms and round to nearerst ms - rounding is important
  // because otherwise the truncation error may accumulate e.g. in sums.
  //
  // Given infinite resolution, this expression could be written as:
  //  trunc((end - start (units:freq*sec))/freq (units:sec) *
  //                1000 (unit:ms) + 1/2 (unit:ms))
  ULONGLONG freq = GetTimerFrequency();
  return ((end_time - start_ticks_) * 1000L + freq / 2) / freq;
}

ULONGLONG HighresTimer::GetElapsedSec() const {
  ULONGLONG end_time = GetCurrentTicks();

  // Scale to ms and round to nearerst ms - rounding is important
  // because otherwise the truncation error may accumulate e.g. in sums.
  //
  // Given infinite resolution, this expression could be written as:
  //  trunc((end - start (units:freq*sec))/freq (unit:sec) + 1/2 (unit:sec))
  ULONGLONG freq = GetTimerFrequency();
  return ((end_time - start_ticks_) + freq / 2) / freq;
}

void HighresTimer::CollectPerfFreq() {
  LARGE_INTEGER freq;

  // Note that this is racy.  It's OK, however, because even
  // concurrent executions of this are idempotent.
  if (::QueryPerformanceFrequency(&freq)) {
    perf_freq_ = freq.QuadPart;
    perf_freq_collected_ = true;
  }
}