// Return a fraction indicating how much of the generation can be treated as
// "dead wood" (i.e., not reclaimed).  The function uses a normal distribution
// based on the density of live objects in the generation to determine a limit,
// which is then adjusted so the return value is min_percent when the density is
// 1.
//
// The following table shows some return values for a different values of the
// standard deviation (ParallelOldDeadWoodLimiterStdDev); the mean is 0.5 and
// min_percent is 1.
//
//                          fraction allowed as dead wood
//         -----------------------------------------------------------------
// density std_dev=70 std_dev=75 std_dev=80 std_dev=85 std_dev=90 std_dev=95
// ------- ---------- ---------- ---------- ---------- ---------- ----------
// 0.00000 0.01000000 0.01000000 0.01000000 0.01000000 0.01000000 0.01000000
// 0.05000 0.03193096 0.02836880 0.02550828 0.02319280 0.02130337 0.01974941
// 0.10000 0.05247504 0.04547452 0.03988045 0.03537016 0.03170171 0.02869272
// 0.15000 0.07135702 0.06111390 0.05296419 0.04641639 0.04110601 0.03676066
// 0.20000 0.08831616 0.07509618 0.06461766 0.05622444 0.04943437 0.04388975
// 0.25000 0.10311208 0.08724696 0.07471205 0.06469760 0.05661313 0.05002313
// 0.30000 0.11553050 0.09741183 0.08313394 0.07175114 0.06257797 0.05511132
// 0.35000 0.12538832 0.10545958 0.08978741 0.07731366 0.06727491 0.05911289
// 0.40000 0.13253818 0.11128511 0.09459590 0.08132834 0.07066107 0.06199500
// 0.45000 0.13687208 0.11481163 0.09750361 0.08375387 0.07270534 0.06373386
// 0.50000 0.13832410 0.11599237 0.09847664 0.08456518 0.07338887 0.06431510
// 0.55000 0.13687208 0.11481163 0.09750361 0.08375387 0.07270534 0.06373386
// 0.60000 0.13253818 0.11128511 0.09459590 0.08132834 0.07066107 0.06199500
// 0.65000 0.12538832 0.10545958 0.08978741 0.07731366 0.06727491 0.05911289
// 0.70000 0.11553050 0.09741183 0.08313394 0.07175114 0.06257797 0.05511132
// 0.75000 0.10311208 0.08724696 0.07471205 0.06469760 0.05661313 0.05002313
// 0.80000 0.08831616 0.07509618 0.06461766 0.05622444 0.04943437 0.04388975
// 0.85000 0.07135702 0.06111390 0.05296419 0.04641639 0.04110601 0.03676066
// 0.90000 0.05247504 0.04547452 0.03988045 0.03537016 0.03170171 0.02869272
// 0.95000 0.03193096 0.02836880 0.02550828 0.02319280 0.02130337 0.01974941
// 1.00000 0.01000000 0.01000000 0.01000000 0.01000000 0.01000000 0.01000000

double PSParallelCompact::dead_wood_limiter(double density, size_t min_percent)
{

  {- -------------------------------------------
  (1) (assert)
      ---------------------------------------- -}

      assert(_dwl_initialized, "uninitialized");

  {- -------------------------------------------
  (1) 引数の density に対し, 
      領域中の (density*100)% が live オブジェクトである確率を計算する (以下の raw_limit).
      ---------------------------------------- -}

      // The raw limit is the value of the normal distribution at x = density.
      const double raw_limit = normal_distribution(density);

  {- -------------------------------------------
  (1) raw_limit の値を少し調整して, 
      density が 1 の場合に結果が min_percent になるようにし (以下の limit), 
      計算結果をリターンする.
      (なお, 値が 0 未満になってしまった場合は, 0.0 をリターンする)
      ---------------------------------------- -}

      // Adjust the raw limit so it becomes the minimum when the density is 1.
      //
      // First subtract the adjustment value (which is simply the precomputed value
      // normal_distribution(1.0)); this yields a value of 0 when the density is 1.
      // Then add the minimum value, so the minimum is returned when the density is
      // 1.  Finally, prevent negative values, which occur when the mean is not 0.5.
      const double min = double(min_percent) / 100.0;
      const double limit = raw_limit - _dwl_adjustment + min;
      return MAX2(limit, 0.0);
    }