after modifying the variable type in class inout, _base in class mh_sampler has a random value but not the assigned value

[QiongwenXu]

In macOS (10.15.2), after modifying the type of input and output in class inout from int to int64_t, _base in class mh_sampler is no longer the assigned value 2, but a random value. In Linux (Ubuntu 18.04), this issue does not occur.
code in inout.cc

class inout {
 public:
  int64_t input;
  int64_t output;
 ......
};

code in mh_sampler.cc

double mh_sampler::cost_to_pi(double cost) {
  // TODO: _base value is not 2 in macos, but 2 in linux
  // return pow(_base, -1.0 * cost);
  return pow(2, -1.0 * cost);

[QiongwenXu]

this problem disappears, but have not found the reason.