background
CRC32, a lightweight verification algorithm, is widely used in embedded development, such as the storage of User data and the storage of non-critical
data (for important data, it is generally not recommended to use only CRC32 to verify its integrity. Consider encryption processing). On the PC side, a scripting
language to generate the CRC32 check value, while on the embedded device side, due to the limited capabilities of the device side, the program written in C will be used directly to
do the CRC32 check;
Python implements CRC32 checksum algorithm
Python implements crc32 (with both md5 and sha1 verification algorithms demo) The algorithm is as follows:
#!/usr/bin/python
import sys
import os
from zlib import crc32
import hashlib
import binascii
def getcrc32(filepath):
file = open(filepath,'rb')
return crc32(file.read())
def getbinasciiCRC(filepath):
file = open(filepath,'rb')
return (binascii.crc32(file.read())&0xffffffff)
def getmd5(filepath):
file = open(filepath,'rb')
md5func = hashlib.md5()
md5func.update(file.read())
return md5func.hexdigest()
def getsha1(filepath):
file = open(filepath,'rb')
sha1func = hashlib.sha1()
sha1func.update(file.read())
return sha1func.hexdigest()
path = sys.argv[1]
print sys.argv[0], " ",path
print "crc32 value:%X"%(getcrc32(path)&0xffffffff)
print "binascii crc32 value:%X"%(getbinasciiCRC(path))
print "md5 value:%s"%(getmd5(path))
print "sha1 value:%s"%(getsha1(path))The python version used in this example is 2.7.4, and the three modules zlib/hashlib/binascii need to be installed. In practical applications, only one of zlib and binascii can be installed, both of which contain the method of calculating crc32;
C implements CRC32 algorithm
Because the computing power on the embedded device side is limited, the usual practice is to use the crc32 table lookup method to calculate crc32, and use the table of 256 elements calculated in advance to calculate crc32 (using polynomial: x^{{32}}+ x^{{26}}+x^{{23}}+x^{{22}}+x^{{16}}+x^{{12}}+x^{{11}}+x^ {{10}}+x^{8}+x^{7}+x^{5}+x^{4}+x^{2}+x+1);
The table generation method implemented in C is as follows:
static unsigned int CRC32_Table[256];
/**
* 产生CRC32查表法所用的表,
* 0xEDB88320:CRC32的生成项是1 0000 0100 1100 0001 0001 1101 1011 0111，去掉最高位的1，保留32bit，然后再颠倒后
* 转换成16进制就是0xEDB88320
*/
static void _createCRCTable(void)
{
unsigned int crc32;
unsigned int idx = 0;
unsigned int bit = 0;
for(idx = 0; idx < 256; idx++)
{
crc32 = idx;
for(bit = 0; bit < 8; bit++)
{
if(crc32&1)
{
crc32 = (crc32 >> 1)^(0xEDB88320);
}
else
{
crc32 = crc32 >> 1;
}
}
CRC32_Table[idx] = crc32;
printf("0x%08x, ", CRC32_Table[idx]);
if((idx+1)%8 == 0)
printf("\n");
}
}Subsequent calculation of CRC32 will directly use the already generated table: CRC32_Table[256]; in formal use, the table can be directly fixed in the code,
as follows:
static const unsigned int CRC32_Table[256] =
{
0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA,
0x076DC419, 0x706AF48F, 0xE963A535, 0x9E6495A3,
0x0EDB8832, 0x79DCB8A4, 0xE0D5E91E, 0x97D2D988,
0x09B64C2B, 0x7EB17CBD, 0xE7B82D07, 0x90BF1D91,
0x1DB71064, 0x6AB020F2, 0xF3B97148, 0x84BE41DE,
0x1ADAD47D, 0x6DDDE4EB, 0xF4D4B551, 0x83D385C7,
0x136C9856, 0x646BA8C0, 0xFD62F97A, 0x8A65C9EC,
0x14015C4F, 0x63066CD9, 0xFA0F3D63, 0x8D080DF5,
0x3B6E20C8, 0x4C69105E, 0xD56041E4, 0xA2677172,
0x3C03E4D1, 0x4B04D447, 0xD20D85FD, 0xA50AB56B,
0x35B5A8FA, 0x42B2986C, 0xDBBBC9D6, 0xACBCF940,
0x32D86CE3, 0x45DF5C75, 0xDCD60DCF, 0xABD13D59,
0x26D930AC, 0x51DE003A, 0xC8D75180, 0xBFD06116,
0x21B4F4B5, 0x56B3C423, 0xCFBA9599, 0xB8BDA50F,
0x2802B89E, 0x5F058808, 0xC60CD9B2, 0xB10BE924,
0x2F6F7C87, 0x58684C11, 0xC1611DAB, 0xB6662D3D,
0x76DC4190, 0x01DB7106, 0x98D220BC, 0xEFD5102A,
0x71B18589, 0x06B6B51F, 0x9FBFE4A5, 0xE8B8D433,
0x7807C9A2, 0x0F00F934, 0x9609A88E, 0xE10E9818,
0x7F6A0DBB, 0x086D3D2D, 0x91646C97, 0xE6635C01,
0x6B6B51F4, 0x1C6C6162, 0x856530D8, 0xF262004E,
0x6C0695ED, 0x1B01A57B, 0x8208F4C1, 0xF50FC457,
0x65B0D9C6, 0x12B7E950, 0x8BBEB8EA, 0xFCB9887C,
0x62DD1DDF, 0x15DA2D49, 0x8CD37CF3, 0xFBD44C65,
0x4DB26158, 0x3AB551CE, 0xA3BC0074, 0xD4BB30E2,
0x4ADFA541, 0x3DD895D7, 0xA4D1C46D, 0xD3D6F4FB,
0x4369E96A, 0x346ED9FC, 0xAD678846, 0xDA60B8D0,
0x44042D73, 0x33031DE5, 0xAA0A4C5F, 0xDD0D7CC9,
0x5005713C, 0x270241AA, 0xBE0B1010, 0xC90C2086,
0x5768B525, 0x206F85B3, 0xB966D409, 0xCE61E49F,
0x5EDEF90E, 0x29D9C998, 0xB0D09822, 0xC7D7A8B4,
0x59B33D17, 0x2EB40D81, 0xB7BD5C3B, 0xC0BA6CAD,
0xEDB88320, 0x9ABFB3B6, 0x03B6E20C, 0x74B1D29A,
0xEAD54739, 0x9DD277AF, 0x04DB2615, 0x73DC1683,
0xE3630B12, 0x94643B84, 0x0D6D6A3E, 0x7A6A5AA8,
0xE40ECF0B, 0x9309FF9D, 0x0A00AE27, 0x7D079EB1,
0xF00F9344, 0x8708A3D2, 0x1E01F268, 0x6906C2FE,
0xF762575D, 0x806567CB, 0x196C3671, 0x6E6B06E7,
0xFED41B76, 0x89D32BE0, 0x10DA7A5A, 0x67DD4ACC,
0xF9B9DF6F, 0x8EBEEFF9, 0x17B7BE43, 0x60B08ED5,
0xD6D6A3E8, 0xA1D1937E, 0x38D8C2C4, 0x4FDFF252,
0xD1BB67F1, 0xA6BC5767, 0x3FB506DD, 0x48B2364B,
0xD80D2BDA, 0xAF0A1B4C, 0x36034AF6, 0x41047A60,
0xDF60EFC3, 0xA867DF55, 0x316E8EEF, 0x4669BE79,
0xCB61B38C, 0xBC66831A, 0x256FD2A0, 0x5268E236,
0xCC0C7795, 0xBB0B4703, 0x220216B9, 0x5505262F,
0xC5BA3BBE, 0xB2BD0B28, 0x2BB45A92, 0x5CB36A04,
0xC2D7FFA7, 0xB5D0CF31, 0x2CD99E8B, 0x5BDEAE1D,
0x9B64C2B0, 0xEC63F226, 0x756AA39C, 0x026D930A,
0x9C0906A9, 0xEB0E363F, 0x72076785, 0x05005713,
0x95BF4A82, 0xE2B87A14, 0x7BB12BAE, 0x0CB61B38,
0x92D28E9B, 0xE5D5BE0D, 0x7CDCEFB7, 0x0BDBDF21,
0x86D3D2D4, 0xF1D4E242, 0x68DDB3F8, 0x1FDA836E,
0x81BE16CD, 0xF6B9265B, 0x6FB077E1, 0x18B74777,
0x88085AE6, 0xFF0F6A70, 0x66063BCA, 0x11010B5C,
0x8F659EFF, 0xF862AE69, 0x616BFFD3, 0x166CCF45,
0xA00AE278, 0xD70DD2EE, 0x4E048354, 0x3903B3C2,
0xA7672661, 0xD06016F7, 0x4969474D, 0x3E6E77DB,
0xAED16A4A, 0xD9D65ADC, 0x40DF0B66, 0x37D83BF0,
0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 0x30B5FFE9,
0xBDBDF21C, 0xCABAC28A, 0x53B39330, 0x24B4A3A6,
0xBAD03605, 0xCDD70693, 0x54DE5729, 0x23D967BF,
0xB3667A2E, 0xC4614AB8, 0x5D681B02, 0x2A6F2B94,
0xB40BBE37, 0xC30C8EA1, 0x5A05DF1B, 0x2D02EF8D
};Calculate CRC32:
/**
* [_getCRC32 使用查表法计算CRC32]
* @param buffer [缓存地址]
* @param bufferLen [缓存长度]
* @return [计算出的CRC32值]
*/
static unsigned int _getCRC32(void *buffer, unsigned int bufferLen)
{
unsigned int crc32Value = 0xffffffff;
unsigned char *pTmpBuffer = buffer;
while(bufferLen--)
{
crc32Value = CRC32_Table[(crc32Value^ *pTmpBuffer++) & 0xff] ^ (crc32Value >> 8);
}
return (crc32Value^0xffffffff);
}
The test function is as follows:
int main(int argc, char *argv[])
{
FILE* pFile = NULL;
void* tmpBuffer = NULL;
unsigned int crc32Value = 0;
char *FilePath[1024];
struct stat fileInfo;
if(argc != 2)
{
printf("The program run format:./crc32bin [filepath] \n");
return -1;
}
printf("open FilePath:%s\n", argv[1]);
strncpy((char*)FilePath, (char*)argv[1], 1023);
if(stat((const char*)FilePath, &fileInfo)<0)
{
printf("Stat file failed!\n");
return -1;
}
printf("file size:%u\n", fileInfo.st_size);
tmpBuffer = malloc((unsigned int)(fileInfo.st_size)+0x10);
if(!tmpBuffer)
{
printf("alloc buffer failed!\n");
return -1;
}
_createCRCTable();
pFile = fopen((const char*)FilePath, "rb+");
fread(tmpBuffer, fileInfo.st_size, 1, pFile);
crc32Value = _getCRC32(tmpBuffer, fileInfo.st_size);
printf("crc32Value is:0x%8x\n", crc32Value);
fclose(pFile);
free(tmpBuffer);
return 0;
}Test the same file, use python and C respectively, the calculated crc32 values are the same, complete!