get_block_template获取任务如下：如何计算head_hash，规则是什么，由于不懂rust语法，看不懂里面的计算逻辑
{
“jsonrpc”: “2.0”,
“result”: {
“bytes_limit”: “1024”,
“cellbase”: {
“cycles”: null,
“data”: {
“cell_deps”: [],
“header_deps”: [],
“inputs”: [{
“previous_output”: {
“index”: “4294967295”,
“tx_hash”: “0x0000000000000000000000000000000000000000000000000000000000000000”
},
“since”: “33849”
}],
“outputs”: [{
“capacity”: “86517358461”,
“lock”: {
“args”: [“0xddc1ddf9c135061b7635ca51e735fc2b03cee339”],
“code_hash”: “0x1892ea40d82b53c678ff88312450bbb17e164d7a3e0a90941aa58839f56f8df2”,
“hash_type”: “type”
},
“type”: null
}],
“outputs_data”: [“0x”],
“version”: “0”,
“witnesses”: [{
“data”: [“0x54811ce986d5c3e57eaafab22cdd080e32209e39590e204a99b32935f835a13c01”, “0xc61a169ab30e7de7ceff6c3a75733d99fe742a8c”]
}]
},
“hash”: “0xaa7f936c172f5fe7e2ae30c726ba44d8ac0a22dd77f43a2a1b3534648f0c17b6”
},
“current_time”: “1568087571117”,
“cycles_limit”: “51673900000”,
“dao”: “0x01000000000000000af1677430652600768065bdfc3b440000ff61346d330100”,
“difficulty”: “0x35a9ae20a27f”,
“epoch”: “22”,
“number”: “33849”,
“parent_hash”: “0x42ec33072ad79065ccf587fa24e2825e93f8688a27862c0bf029b2dac9491956”,
“proposals”: [],
“transactions”: [],
“uncles”: [],
“uncles_count_limit”: “2”,
“version”: “0”,
“work_id”: “0”
},
“id”: 2
}