python bbc校验 python crc校验函数

 

binascii.crc32(s [,crc])

返回CRC32校验。参数'crc'指定初始值用于循环。例如：

 

Code
>>> import binascii
>>> crc = binascii.crc32('spam')
>>> binascii.crc32(' and eggs', crc)
739139840
>>> binascii.crc32('spam and eggs')
739139840

 

 

Code
import binascii 

def getFileCRC(_path): 
    try: 
        blocksize = 1024 * 64 
        f = open(_path,"rb") 
        str = f.read(blocksize) 
        crc = 0 
        while(len(str) != 0): 
            crc = binascii.crc32(str, crc) 
            str = f.read(blocksize) 
        f.close() 
    except: 
        print 'get file crc error!' 
        return 0 
    return crc

 

 

Code
python 2.X的crc32實作上跟一般的C實作上在整數有號無號的處理上略有不同, 所以使用python 2.X與一般C實作算出的crc32(如sfv)比對時,通常需要特別的方法,

這邊列出一個透過zlib.crc32快速得到所需要結果的方法：

import zlib

def crc32(st):
    crc = zlib.crc32(st)
    if crc > 0:
      return "%x" % (crc)
    else:
      return "%x" % (~crc ^ 0xffffffff)

ex1 = "12345"
ex2 = "1kcaseztsa12345azy"

print "%x" % zlib.crc32(ex1)
print crc32(ex1)
print "%x" % zlib.crc32(ex2)
print crc32(ex2)

或如果你有ctypes的話:

import zlib
import ctypes

def crc32_c(st):
    return "%x" % ctypes.c_uint32(zlib.crc32(st)).value

ex1 = "12345"
ex2 = "1kcaseztsa12345azy"

print "%x" % zlib.crc32(ex1)
print crc32_c(ex1)
print "%x" % zlib.crc32(ex2)
print crc32_c(ex2)

註： python 3.0以上沒有這個問題.

 

 

Code
from ctypes import * 
import binascii 

def getFileCRC(_path): 
try: 
blocksize = 1024 * 64 
f = open(_path,"rb") 
str = f.read(blocksize) 
crc = 0 
while(len(str) != 0): 
crc = binascii.crc32(str, crc) 
str = f.read(blocksize) 
f.close() 
except: 
klog.error("get file crc error!") 
return 0 
return c_uint(crc).value