Python實現CRC校驗
阿新 • • 發佈:2019-01-03
<pre name="code" class="python"><span style="font-family: Arial, Helvetica, sans-serif; background-color: rgb(255, 255, 255);">參考網址http://blog.163.com/[email protected]/blog/static/107495394201075114028606/</span>
上邊參考網址內的計算方法親自算一遍就知道CRC怎麼使用了(就是上邊的圖片),搜尋了一下,大部分都是C語言實現,工作期間需要用Python實現求字串CRC校驗的函式,使用查表法實現
#!/usr/bin/env python # -*- coding: utf-8 -*- POLYNOMIAL = 0x1021 INITIAL_REMAINDER = 0xFFFF FINAL_XOR_VALUE = 0x0000 WIDTH = 16 TOPBIT = (1 << (WIDTH - 1)) crcTable = {} def crcInit(): SHIFT = WIDTH - 8 for step in range(0, 256): remainder = step << SHIFT for bit in range(8, 0, -1): if remainder & TOPBIT: remainder = ((remainder << 1) & 0xFFFF) ^ 0x1021 else: remainder = remainder << 1 crcTable[step] = remainder def crcFast(message, nBytes): crcInit() remainder = 0xFFFF data = 0 byte = 0 while byte < nBytes: data = ord(message[byte]) ^ (remainder >> (WIDTH - 8)) remainder = crcTable[data] ^ ((remainder << 8)&0xFFFF) byte = byte + 1 return hex(remainder)[2: ]
位移時要注意 python的整數沒有最大值,而C++中不同,左移會將高位移掉,python則一直保留高位,所以通過位0xFFFF與的方式將高位去掉。