crc32.c

CRC32多项式实现

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define false 0
#define true 1

char crc_table_is_init = false;
unsigned int crc_table[256];
typedef struct headdef
{
	char name[10];
	int id;
	int crc;
}HEAD,*LPHEAD;
unsigned int crc32(char *buf, long len)
{
	unsigned int crc = 0;

	if (!crc_table_is_init) {
		unsigned int i, j, h = 1;
		crc_table_is_init = true;
		crc_table[0] = 0;
		for (i = 128; i; i >>= 1) {
			h = (h >> 1) ^ ((h & 1) ? (int)0xedb88320 : 0);
			for (j = 0; j < 256; j += 2*i)
			crc_table[i+j] = crc_table[j] ^ h;
		}
	}

	crc ^= 0xffffffff;
	while (len--)
	crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
	return crc ^ 0xffffffff;
}
void main()
{
	int a;
	HEAD test;
	strcpy(test.name,"betty");
	test.id=1;
	test.crc=crc32(&test,sizeof(HEAD)-4);
	//a=	crc32(&test,sizeof(HEAD));
	printf("a=%x\n",test.crc);
}