#include <stdlib.h>
#include <io.h>
#define alt_8 char
#define alt_u8 unsigned char
#define alt_32 int
#define alt_u32 unsigned int
#define alt_64 long long
#define alt_u64 unsigned long long
//位翻转函数
alt_u64 Reflect(alt_u64 ref, alt_u8 ch)
{
int i;
alt_u64 value = 0;
for (i = 1; i < (ch + 1); i++)
{
if (ref & 1)
value |= 1 << (ch – i);
ref >>= 1;
}
return value;
}
//标准的CRC32多项式
#define poly 0x04C11DB7
//翻转的CRC32多项式
#define upoly 0xEDB88320
alt_u32 crc32_bit(alt_u8 *ptr, alt_u32 len, alt_u32 gx)
{
alt_u8 i;
alt_u32 crc = 0xffffffff;
while (len–)
{
for (i = 1; i != 0; i <<= 1)
{
if ((crc & 0x80000000) != 0)
{
crc <<= 1;
crc ^= gx;
}
else
crc <<= 1;
if ((*ptr & i) != 0)
crc ^= gx;
}
ptr++;
}
return (Reflect(crc, 32) ^ 0xffffffff);
}
alt_u32 Table1[256];
alt_u32 Table2[256];
// 生成CRC32 普通表 , 第二项是04C11DB7
void gen_direct_table(alt_u32 *table)
{
alt_u32 gx = 0x04c11db7;
unsigned long i32, j32;
unsigned long nData32;
unsigned long nAccum32;
for (i32 = 0; i32 < 256; i32++)
{
nData32 = (unsigned long)(i32 << 24);
nAccum32 = 0;
for (j32 = 0; j32 < 8; j32++)
{
if ((nData32 ^ nAccum32) & 0x80000000)
nAccum32 = (nAccum32 << 1) ^ gx;
else
nAccum32 <<= 1;
nData32 <<= 1;
}
table[i32] = nAccum32;
}
}
// 生成CRC32 翻转表 第二项是77073096
void gen_normal_table(alt_u32 *table)
{
alt_u32 gx = 0x04c11db7;
alt_u32 temp, crc;
for (int i = 0; i <= 0xFF; i++)
{
temp = Reflect(i, 8);
table[i] = temp << 24;
for (int j = 0; j < 8; j++)
{
unsigned long int t1, t2;
unsigned long int flag = table[i] & 0x80000000;
t1 = (table[i] << 1);
if (flag == 0)
t2 = 0;
else
t2 = gx;
table[i] = t1^t2;
}
crc = table[i];
table[i] = Reflect(table[i], 32);
}
}
alt_u32 DIRECT_TABLE_CRC(alt_u8 *ptr, int len, alt_u32 * table)
{
alt_u32 crc = 0xffffffff;
alt_u8 *p = ptr;
int i;
for (i = 0; i < len; i++)
crc = (crc << 8) ^ table[(crc >> 24) ^ (alt_u8)Reflect((*(p + i)), 8)];
return ~(alt_u32)Reflect(crc, 32);
}
alt_u32 Reverse_Table_CRC(alt_u8 *data, alt_32 len, alt_u32 * table)
{
alt_u32 crc = 0xffffffff;
alt_u8 *p = data;
int i;
for (i = 0; i <len; i++)
crc = table[(crc ^ (*(p + i))) & 0xff] ^ (crc >> 8);
return ~crc;
}
//这是一个完整的以太网帧。最后四个字节 8b 6b f5 13是其FCS字段，用于与后面生成的CRC32对照
alt_u8 tx_data[] = {
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x00, 0x1f, //8
0x29, 0x00, 0xb5, 0xfa, 0x08, 0x06, 0x00, 0x01, //15
0x08, 0x00, 0x06, 0x04, 0x00, 0x01, 0x00, 0x1f, //24
0x29, 0x00, 0xb5, 0xfa, 0xac, 0x15, 0x0e, 0xd9, //32
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xac, 0x15, //40
0x0e, 0x8e, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, //48
0x00, 0x00 , 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, //56
0x00, 0x00, 0x00, 0x00, 0x8b, 0x6b, 0xf5, 0x13 //64
};
int main()
{
alt_u8 *data = tx_data;
alt_u32 dataLen = sizeof(tx_data) – 4;
int sum = 256;
int i = 0;
//生成普通表，用于直接计算的表
gen_direct_table(Table1);
printf(“Table1 :\n”);
for (i = 0; i < sum; i++)
{
if (i<16)
printf(“%08x “, Table1[i]);
}
printf(“\n\n”);
//生成翻转表，是官方推荐的，故称其为normal_table
gen_normal_table(Table2);
printf(“Table2 :\n”);
for (i = 0; i < sum; i++)
{
if (i<16)
printf(“%08x “, Table2[i]);
}
printf(“\n\n”);
printf(“dataLen = %d\n”, dataLen);//打印数据长度，应该是60字节。
//计算并打印出CRC32校验码，应该是0x13f56b8b
//按照bit进行校验，最慢
printf(“Slow CRC by bit : %08x\n”, crc32_bit(data, dataLen, 0x04c11db7));
//使用普通表，非官方，很慢
printf(“Direct Table ref + xor : %08x\n”, DIRECT_TABLE_CRC(data, dataLen, Table1));
//使用翻转表，官方推荐的，很快
printf(“Reverse Table ref + xor : %08x\n”, Reverse_Table_CRC(data, dataLen, Table2));
system(“pause”);
return 0;
}