Occasional errors in fields::process_incoming_chunk_data from multiplying two std::complex<realnum> numbers

[oskooi]

Occasionally, I detect errors in the unit test python/tests/test_refl_angular.py which is traced to line 190 of fields::process_incoming_chunk_data involving the multiplication of two complex numbers:

meep/src/step.cpp

Lines 172 to 196 in dad3e52

	void fields::process_incoming_chunk_data(field_type ft, const chunk_pair &comm_pair) {
	am_now_working_on(Boundaries);
	int this_chunk_idx = comm_pair.second;
	const int pair_idx = chunk_pair_to_index(comm_pair);
	const realnum *pair_comm_block = static_cast<realnum *>(comm_blocks[ft][pair_idx]);
	{
	const comms_key key = {ft, CONNECT_PHASE, comm_pair};
	size_t num_transfers = get_comm_size(key) / 2; // Two realnums per complex
	if (num_transfers) {
	const std::complex<realnum> *pair_comm_block_complex =
	reinterpret_cast<const std::complex<realnum> *>(pair_comm_block);
	const std::vector<realnum *> &incoming_connection =
	chunks[this_chunk_idx]->connections_in.at(key);
	const std::vector<std::complex<realnum> > &connection_phase_for_ft =
	chunks[this_chunk_idx]->connection_phases[key];
	for (size_t n = 0; n < num_transfers; ++n) {
	std::complex<realnum> temp = connection_phase_for_ft[n] * pair_comm_block_complex[n];
	*(incoming_connection[2 * n]) = temp.real();
	*(incoming_connection[2 * n + 1]) = temp.imag();
	}
	pair_comm_block += 2 * num_transfers;
	}
	}

The problem, I suspect, is actually in the call to reinterpret_cast which is supposed to convert const realnum to const std::complex<realnum> and then use the result in the multiplication on line 190:

meep/src/step.cpp

Lines 182 to 183 in dad3e52

	const std::complex<realnum> *pair_comm_block_complex =
	reinterpret_cast<const std::complex<realnum> *>(pair_comm_block);

A snippet of the stack trace shows where the error is triggered:

...
on time step 103902 (time=129.877), 0.00696845 s/step
on time step 104413 (time=130.516), 0.00783793 s/step
on time step 105022 (time=131.278), 0.00657031 s/step
*** SIGTERM received by PID 1500 (TID 1500) on cpu 68 from PID 1; stack trace: ***
PC: @     0x556870995664  (unknown)  std::__u::operator*<>()
    @     0x55688065707a       1152  FailureSignalHandler()
    @     0x7f9de4deb1c0  (unknown)  (unknown)
    @     0x556870995664          8  std::__u::operator*<>()
    @     0x556870a15111        128  meep::fields::process_incoming_chunk_data()
    @     0x556870a14edd        208  meep::fields::step_boundaries()
    @     0x556870a141f1        112  meep::fields::step()
    @     0x7f9dde21fbaf         80  _wrap_fields_step()
    @     0x55688052b589         32  cfunction_call
    @     0x5568804e860d         96  _PyObject_MakeTpCall
    @     0x5568805ecbe1        112  call_function
    @     0x5568805e8866        400  _PyEval_EvalFrameDefault
    @     0x5568805e3aa4         48  _PyEval_Vector
...