#include "crc.h"
//#include <stdio.h> //用于验证和生成CRC_Table

//X8+X4+X3+X2+1 -> 0X1D -> POLY=B8
static const unsigned char crc_table[] =
{
0x00, 0xb8, 0xc8, 0x70, 0x28, 0x90, 0xe0, 0x58, 0x50, 0xe8, 0x98, 0x20, 0x78, 0xc0, 0xb0, 0x08, 
0xa0, 0x18, 0x68, 0xd0, 0x88, 0x30, 0x40, 0xf8, 0xf0, 0x48, 0x38, 0x80, 0xd8, 0x60, 0x10, 0xa8, 
0xf8, 0x40, 0x30, 0x88, 0xd0, 0x68, 0x18, 0xa0, 0xa8, 0x10, 0x60, 0xd8, 0x80, 0x38, 0x48, 0xf0, 
0x58, 0xe0, 0x90, 0x28, 0x70, 0xc8, 0xb8, 0x00, 0x08, 0xb0, 0xc0, 0x78, 0x20, 0x98, 0xe8, 0x50, 
0x48, 0xf0, 0x80, 0x38, 0x60, 0xd8, 0xa8, 0x10, 0x18, 0xa0, 0xd0, 0x68, 0x30, 0x88, 0xf8, 0x40, 
0xe8, 0x50, 0x20, 0x98, 0xc0, 0x78, 0x08, 0xb0, 0xb8, 0x00, 0x70, 0xc8, 0x90, 0x28, 0x58, 0xe0, 
0xb0, 0x08, 0x78, 0xc0, 0x98, 0x20, 0x50, 0xe8, 0xe0, 0x58, 0x28, 0x90, 0xc8, 0x70, 0x00, 0xb8, 
0x10, 0xa8, 0xd8, 0x60, 0x38, 0x80, 0xf0, 0x48, 0x40, 0xf8, 0x88, 0x30, 0x68, 0xd0, 0xa0, 0x18, 
0x90, 0x28, 0x58, 0xe0, 0xb8, 0x00, 0x70, 0xc8, 0xc0, 0x78, 0x08, 0xb0, 0xe8, 0x50, 0x20, 0x98, 
0x30, 0x88, 0xf8, 0x40, 0x18, 0xa0, 0xd0, 0x68, 0x60, 0xd8, 0xa8, 0x10, 0x48, 0xf0, 0x80, 0x38, 
0x68, 0xd0, 0xa0, 0x18, 0x40, 0xf8, 0x88, 0x30, 0x38, 0x80, 0xf0, 0x48, 0x10, 0xa8, 0xd8, 0x60, 
0xc8, 0x70, 0x00, 0xb8, 0xe0, 0x58, 0x28, 0x90, 0x98, 0x20, 0x50, 0xe8, 0xb0, 0x08, 0x78, 0xc0, 
0xd8, 0x60, 0x10, 0xa8, 0xf0, 0x48, 0x38, 0x80, 0x88, 0x30, 0x40, 0xf8, 0xa0, 0x18, 0x68, 0xd0, 
0x78, 0xc0, 0xb0, 0x08, 0x50, 0xe8, 0x98, 0x20, 0x28, 0x90, 0xe0, 0x58, 0x00, 0xb8, 0xc8, 0x70, 
0x20, 0x98, 0xe8, 0x50, 0x08, 0xb0, 0xc0, 0x78, 0x70, 0xc8, 0xb8, 0x00, 0x58, 0xe0, 0x90, 0x28, 
0x80, 0x38, 0x48, 0xf0, 0xa8, 0x10, 0x60, 0xd8, 0xd0, 0x68, 0x18, 0xa0, 0xf8, 0x40, 0x30, 0x88,
};

unsigned char CRC_Calc(unsigned char * dataptr,unsigned char len)
{
    unsigned char i; 
    unsigned char crc=0xFF; // 计算的初始crc值   

    while(len--)
    {
        crc ^= *dataptr++;  // 每次先与需要计算的数据异或,计算完指向下一数据    
        for (i=0; i<8; i++)   // 下面这段计算过程与计算一个字节crc一样    
        { 
            if (crc & 0x80)	// 判断最高位是否为1  
            // 最高位为1，不需要异或，往左移一位，然后与0x31异或  
			// 0x31(多项式：x8+x5+x4+1，100110001)，最高位不需要异或，直接去掉  
            //X8+X4+X3+X2+1 -> 0X1D -> B8
                crc = (crc << 1) ^ 0xB8;
            else
                crc = (crc << 1);
        }
    }

    return (crc^0XFF); 
}


unsigned char CRC_Calc_Table(unsigned char * dataptr,unsigned char len)
{
    unsigned char  crc = 0xFF;

    while (len--)
    {
        crc = crc_table[crc ^ *dataptr++];
    }
    return (crc^0XFF);
}


//以下程序用于验证和生成CRC_Table
/*
unsigned char cal_table_high_first(unsigned char value)
{
    unsigned char i, crc;

    crc = value;
    //数据往左移了8位，需要计算8次
    for (i=0; i<8; i++)
    { 
        if (crc & 0x80)  //判断最高位是否为1
        {
        //最高位为1，不需要异或，往左移一位，然后与0x31异或  
        //0x31(多项式：x8+x5+x4+1，100110001)，最高位不需要异或，直接去掉  
        //X8+X4+X3+X2+1 -> 0X1D -> B8
            crc = (crc << 1) ^ 0xB8;        }
        else
        {
            //最高位为0时，不需要异或，整体数据往左移一位  
            crc = (crc << 1);
        }
    }

    return crc;
}

//计算crc_Table 
void  create_crc_table(void)
{
    unsigned short i;
    unsigned char j;

    for (i=0; i<=0xFF; i++)
    {
        if (0 == (i%16))
            printf("\n");

        j = i&0xFF;
        printf("0x%.2x, ", cal_table_high_first (j));  //依次计算每个字节的crc校验值 
    }
    printf("\n");
}


int main()
{
    unsigned char TestArr[] = {0x00,0x15,0x22,0x11,0xff,0x13,0x66};
    unsigned char crc;
    create_crc_table();
    printf("crc_data = {0x00,0x15,0x22,0x11,0xff,0x13,0x66}\n");
    crc = CRC_Calc(TestArr,7);
    printf("CRC_Calc       = 0x%x \n",crc);
    crc = CRC_Calc_Table(TestArr,7);
	printf("CRC_Calc_Table = 0x%x \n",crc);
    return 0;
}
*/