etclabscore/cpp-etchash can not search solution by search_light

[caiqinghua]

int epoch_number = block_number / 30000;
const struct ethash_epoch_context *context = ethash_get_global_epoch_context(epoch_number); ethash::search_result ethash_result = ethash::search_light(*context, header_hash, boundary, nonce, 1); if (!ethash_result.solution_found) { return LOW_DIFFICULTY; }

The code can search solution for ethereum, but can not for etc node and cpp-etchash code. Please help me @q9f @iquidus