python计算excel crc_查表法计算crc的python演示程序 | 学步园

#coding=gbk

'''''演示计算crc查找表方法，使用crc-itu 即0x11021

由于crc是在接收和发送位流的同时进行模2除法运算，而发送和接收时都是从低位开始

所以实际上进行查表计算时要注意位顺序的问题。

计算查找表时将生成式进行位反转，并从低位开始异或可使实际查表时不用进行位反转

如果是16位的crc，计算crc最后的结果是一个16位的值，将它附加到数据后时要注意字节顺序，

应该把低字节放在前面，高字节放在后面

在小端模式的处理器上直接赋值不会有问题，在大端模式下则须注意'''

defcrcTable(seed=0x11021):

'''''计算crc查找表'''

#计算位宽，必须是9位(crc8)或17(crc16)位,同时进行位反转

bitWidth=0

rseed=0

whileseed!=0:

bitWidth+=1

rseed<<=1

ifseed&1!=0:

rseed|=1

seed>>=1

ifbitWidthnotin(8,9,16,17):

print'错误的位宽。本程序只接收8+1位或16+1位的crc值'

returnNone

ifbitWidthin(8,16):#用户提供的是简化的crc生成式，需要把最高位的1补上

rseed<<=1

rseed+=1

loop1=0

table=[]

whileloop1<256:

res=loop1#存放结果的数

loop1+=1

loop2=8#一共要进行8次移位

whileloop2:

loop2-=1

ifres&1:

res=res^rseed

res>>=1

table.append(res)

returntable

#-------------------------------------------------------------------------------

defcrcCal(Tar , Table=None):

'''''查表法计算crc值，利用给定的表格，计算目标字符串的crc值

该函数可以计算8位或16位的crc值'''

ifTable==None:

Table=crcTable()

iflen(Table)!=256:

print"表格长度必须为256"

loop1=0

whileloop1<256:

ifTable[loop1]<0orTable[loop1]>65535:

print"表格内的数据必须为16位无符号数"

returnNone

loop1+=1

res=0

forbinTar:

ifisinstance(b,str):

b=ord(b)

ifnot0<=b<256:

print"目标元素必须为0－255之间的数"

returnNone

#该过程可以兼容16位和8位crc的操作，因为8位crc的表格高字节是0

#异或以后不影响值。如果专门为8位编写，则可以更加简单，

cb=res&0xff

cb^=b

#查表，如果只考虑8位crc，直接使用 res=Table[cb]即可

cb=Table[cb]

res>>=8

res^=cb

returnres

#-------------------------------------------------------------------------------

defcrcCalS(Tar , seed=0x11021):

'''''使用移位法计算crc值，结果可与使用查表法的相比较'''

bitWidth=0

rseed=0

whileseed!=0:

bitWidth+=1

rseed<<=1

ifseed&1!=0:

rseed|=1

seed>>=1

ifbitWidthnotin(8,9,16,17):

print'错误的位宽。本程序只接收8+1位或16+1位的crc值'

returnNone

ifbitWidthin(8,16):#用户提供的是简化的crc生成式，需要把最高位的1补上

rseed<<=1

rseed+=1

length=len(Tar)

newTar=[]

forbinTar:

ifisinstance(b,str):

b=ord(b)

ifnot0<=b<256:

print"目标元素必须为0－256之间的数"

returnNone

newTar.append(b)

newTar.extend([0,0])#在尾部补0

res=newTar[0]+newTar[1]*256

loop1=0

whileloop1

res+=(newTar[loop1+2]&0xff)<<16

res=int(res)

loop1+=1

loop2=8

whileloop2:

loop2-=1

ifres&1:

res^=rseed

res>>=1

returnres&0xffff

#-------------------------------------------------------------------------------

if__name__=='__main__':

table=crcTable()

loop=0

print__doc__

print'''''演示crc查找表的生成，生成式为0x11021 ,  他的结果应该是：

0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf,

0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,

0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,

0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,

0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd,

0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,

0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,

0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,

0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,

0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,

0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a,

0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,

0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9,

0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,

0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,

0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,

0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7,

0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,

0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036,

0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,

0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,

0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd,

0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134,

0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,

0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3,

0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb,

0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,

0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,

0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1,

0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,

0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330,

0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78

实际值为 crcTable(0x11021)='''

whileloop<256:

s="%x"%table[loop]

ifloop%8==7:

print"0x%s"%s.zfill(4),','

else:

print"0x%s"%s.zfill(4),',',

loop+=1

test=[255,255]

crc=crcCal(test,table)

print"/n以[0xff,0xff]测试,它的输出应该是0xf0b8, /n实际值是 crcCal([255,255]) =",hex(crc)

crc=crcCalS(test)

print"/tcrcCalS([255,255])=",hex(crc)