CRC-32

#include<stdio.h>
#include<stdint.h>
#include<string.h>
#include<time.h> 
static uint32_t poly = 0x04C11DB7; //多项式函数

//用无符号整型unsigned int 模拟32位寄存器 
uint32_t crc32(char * str, int len)
{
	uint32_t poly = 0x04C11DB7;  //多项式函数 
	uint32_t data = 0xffffffff; //初始化寄存器 
	int i = 0;
	for (i = 0; i < len; i++)
	{
		data ^= str[i]<<24; //由高字节向低字节循环处理 
		int j = 0;a
		for (j = 0; j < 8; j++)
		{
			if (data & 0x80000000) //最高位为1，就与多项式进行异或
				data = (data << 1) ^ poly;
			else
				data <<= 1;       
		}
	}
	return data ^ 0xffffffff; //反转运算 
} 
//int main() {
//	//生成CRC32表 
//	//generate_crc32_table();
//	uint32_t crc32_table_res = 0;
//	char** str = {"Hello, CRC32!","Satisfaction","Technology","Wonderful","Efficiency","Innovation","Destination","Championship",
//					"Celebration","Experience","Adventure","Inspiration","Leadership","Motivation","Creativity","Opportunity",
//					"Progressive","Collaboration","Entrepreneur","Revolution","Transformation"};
//	int i = 0;
//	for (i = 0; i < 21; i++){
//		int len = strlen(&*(str+i));
//		crc32_table_res = crc32(&*(str+i), len);
//		printf("Hello, CRC32!：%X\n", crc32_table_res);
//	}
//	return 0;
//}
int main() {
	
	clock_t begin, end;
	double cost;
	begin = clock();
	//char* str = "Hello, CRC32!";
	char* str = "Life is too short to spend time with people who suck the happiness out of you. If someone wants you in their life, they’ll make room for you. You shouldn’t have to fight for a spot. Never, ever insist yourself to someone who continuously overlooks your worth. And remember, it’s not the people that stand by your side when you’re at your best, but the ones who stand beside you when you’re at your worst that are your true friends.";
	int len = strlen(str);
	uint32_t crc = crc32(str, len);
	int i = 0;
	for (i = 0; i < 1000000; i++)
		crc = crc32(str, len);
	end = clock();
	printf("Hello, CRC32!：%X\n", crc);
	cost = (double)(end - begin)/CLOCKS_PER_SEC;
    printf("constant CLOCKS_PER_SEC is: %ld\n, time cost is: %lf secs\n", CLOCKS_PER_SEC, cost);
	return 0;
}

查表法

#include<stdio.h>
#include<stdint.h>
#include<string.h>
#include<time.h>
static uint32_t poly = 0x04C11DB7;  //多项式函数 
static uint32_t crc32_table[256] = {
0x00000000, 0x04c11db7, 0x09823b6e, 0x0d4326d9, 0x130476dc, 0x17c56b6b, 0x1a864db2, 0x1e475005,
0x2608edb8, 0x22c9f00f, 0x2f8ad6d6, 0x2b4bcb61, 0x350c9b64, 0x31cd86d3, 0x3c8ea00a, 0x384fbdbd,
0x4c11db70, 0x48d0c6c7, 0x4593e01e, 0x4152fda9, 0x5f15adac, 0x5bd4b01b, 0x569796c2, 0x52568b75,
0x6a1936c8, 0x6ed82b7f, 0x639b0da6, 0x675a1011, 0x791d4014, 0x7ddc5da3, 0x709f7b7a, 0x745e66cd,
0x9823b6e0, 0x9ce2ab57, 0x91a18d8e, 0x95609039, 0x8b27c03c, 0x8fe6dd8b, 0x82a5fb52, 0x8664e6e5,
0xbe2b5b58, 0xbaea46ef, 0xb7a96036, 0xb3687d81, 0xad2f2d84, 0xa9ee3033, 0xa4ad16ea, 0xa06c0b5d,
0xd4326d90, 0xd0f37027, 0xddb056fe, 0xd9714b49, 0xc7361b4c, 0xc3f706fb, 0xceb42022, 0xca753d95,
0xf23a8028, 0xf6fb9d9f, 0xfbb8bb46, 0xff79a6f1, 0xe13ef6f4, 0xe5ffeb43, 0xe8bccd9a, 0xec7dd02d,
0x34867077, 0x30476dc0, 0x3d044b19, 0x39c556ae, 0x278206ab, 0x23431b1c, 0x2e003dc5, 0x2ac12072,
0x128e9dcf, 0x164f8078, 0x1b0ca6a1, 0x1fcdbb16, 0x018aeb13, 0x054bf6a4, 0x0808d07d, 0x0cc9cdca,
0x7897ab07, 0x7c56b6b0, 0x71159069, 0x75d48dde, 0x6b93dddb, 0x6f52c06c, 0x6211e6b5, 0x66d0fb02,
0x5e9f46bf, 0x5a5e5b08, 0x571d7dd1, 0x53dc6066, 0x4d9b3063, 0x495a2dd4, 0x44190b0d, 0x40d816ba,
0xaca5c697, 0xa864db20, 0xa527fdf9, 0xa1e6e04e, 0xbfa1b04b, 0xbb60adfc, 0xb6238b25, 0xb2e29692,
0x8aad2b2f, 0x8e6c3698, 0x832f1041, 0x87ee0df6, 0x99a95df3, 0x9d684044, 0x902b669d, 0x94ea7b2a,
0xe0b41de7, 0xe4750050, 0xe9362689, 0xedf73b3e, 0xf3b06b3b, 0xf771768c, 0xfa325055, 0xfef34de2,
0xc6bcf05f, 0xc27dede8, 0xcf3ecb31, 0xcbffd686, 0xd5b88683, 0xd1799b34, 0xdc3abded, 0xd8fba05a,
0x690ce0ee, 0x6dcdfd59, 0x608edb80, 0x644fc637, 0x7a089632, 0x7ec98b85, 0x738aad5c, 0x774bb0eb,
0x4f040d56, 0x4bc510e1, 0x46863638, 0x42472b8f, 0x5c007b8a, 0x58c1663d, 0x558240e4, 0x51435d53,
0x251d3b9e, 0x21dc2629, 0x2c9f00f0, 0x285e1d47, 0x36194d42, 0x32d850f5, 0x3f9b762c, 0x3b5a6b9b,
0x0315d626, 0x07d4cb91, 0x0a97ed48, 0x0e56f0ff, 0x1011a0fa, 0x14d0bd4d, 0x19939b94, 0x1d528623,
0xf12f560e, 0xf5ee4bb9, 0xf8ad6d60, 0xfc6c70d7, 0xe22b20d2, 0xe6ea3d65, 0xeba91bbc, 0xef68060b,
0xd727bbb6, 0xd3e6a601, 0xdea580d8, 0xda649d6f, 0xc423cd6a, 0xc0e2d0dd, 0xcda1f604, 0xc960ebb3,
0xbd3e8d7e, 0xb9ff90c9, 0xb4bcb610, 0xb07daba7, 0xae3afba2, 0xaafbe615, 0xa7b8c0cc, 0xa379dd7b,
0x9b3660c6, 0x9ff77d71, 0x92b45ba8, 0x9675461f, 0x8832161a, 0x8cf30bad, 0x81b02d74, 0x857130c3,
0x5d8a9099, 0x594b8d2e, 0x5408abf7, 0x50c9b640, 0x4e8ee645, 0x4a4ffbf2, 0x470cdd2b, 0x43cdc09c,
0x7b827d21, 0x7f436096, 0x7200464f, 0x76c15bf8, 0x68860bfd, 0x6c47164a, 0x61043093, 0x65c52d24,
0x119b4be9, 0x155a565e, 0x18197087, 0x1cd86d30, 0x029f3d35, 0x065e2082, 0x0b1d065b, 0x0fdc1bec,
0x3793a651, 0x3352bbe6, 0x3e119d3f, 0x3ad08088, 0x2497d08d, 0x2056cd3a, 0x2d15ebe3, 0x29d4f654,
0xc5a92679, 0xc1683bce, 0xcc2b1d17, 0xc8ea00a0, 0xd6ad50a5, 0xd26c4d12, 0xdf2f6bcb, 0xdbee767c,
0xe3a1cbc1, 0xe760d676, 0xea23f0af, 0xeee2ed18, 0xf0a5bd1d, 0xf464a0aa, 0xf9278673, 0xfde69bc4,
0x89b8fd09, 0x8d79e0be, 0x803ac667, 0x84fbdbd0, 0x9abc8bd5, 0x9e7d9662, 0x933eb0bb, 0x97ffad0c,
0xafb010b1, 0xab710d06, 0xa6322bdf, 0xa2f33668, 0xbcb4666d, 0xb8757bda, 0xb5365d03, 0xb1f740b4
};
/* 
//生成CRC_32_Table 
void generate_crc32_table() {
	uint32_t tmp = 0;
	uint32_t i, j;
//	uint32_t data = 0xffffffff; //初始化寄存器
	
	for (i = 0; i < 256; i++) {
		tmp = i << 24;
		for (j = 0; j < 8; j++) {
			if (tmp & 0x80000000) 
				tmp = (tmp << 1) ^ poly;
			else 
				tmp <<= 1;	
		}
		crc32_table[i] = tmp;
	}
	for (i = 0; i < 256; i++) {
		printf("0x%X, ",crc32_table[i]);
		if ((i + 1) % 8 == 0) {
			printf("\n");
		}
	}
}
*/ 
uint32_t crc32(const char* str, int len) {
	uint32_t data = 0xffffffff; //初始化寄存器 
	int i = 0;
	for (i = 0; i < len; i++) {
		data = ((data & 0x00ffffff) << 8)  ^ crc32_table[(data >> 24) ^ (str[i]) & 0xff];
		//前面是保留处理后的字节 
		//后面由高位向低位处理，然后下标需要右移24位来处理 
	}
	return data ^ 0xffffffff;
}

int main() {
	//生成CRC32表 
	//generate_crc32_table();
	clock_t begin, end;
	double cost;
	begin = clock();
	uint32_t crc32_table_res = 0;
	char* str = "Life is too short to spend time with people who suck the happiness out of you. If someone wants you in their life, they’ll make room for you. You shouldn’t have to fight for a spot. Never, ever insist yourself to someone who continuously overlooks your worth. And remember, it’s not the people that stand by your side when you’re at your best, but the ones who stand beside you when you’re at your worst that are your true friends.";
	int len = strlen(str);
	int i = 0;
	for (i = 0; i < 1000000; i++){
		crc32_table_res = crc32(str, len);
	
	}
	end = clock();
	printf("Hello, CRC32!：%X\n", crc32_table_res);
	cost = (double)(end - begin)/CLOCKS_PER_SEC;
    printf("constant CLOCKS_PER_SEC is: %ld\n, time cost is: %lf secs\n", CLOCKS_PER_SEC, cost);
	
	return 0;
}