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#include "stdio.h"
#include "stdlib.h"

/**
 * @brief CheckSum8计算
 * @param cksum : 计算结果初始值,一般为0
 * @param pBuffer : 数据缓存
 * @param size : 数据长度
 * @return CheckSum8计算结果
*/
unsigned short CheckSum8(unsigned int cksum, void *pBuffer,  int size)
{
    char num = 0;
    unsigned char *p = (unsigned char *)pBuffer;
 
    if ((NULL == pBuffer) || (0 == size))
    {
        return cksum;
    }
   
    while (size > 1)
    {
        cksum += ((unsigned short)p[num] << 8 & 0xff00) | (unsigned short)p[num + 1] & 0x00FF;
        size  -= 2;
        num   += 2;
    }
   
	if (size > 0)
    {
        cksum += ((unsigned short)p[num] << 8) & 0xFFFF;
        num += 1;
    }
 
    while (cksum >> 16)
    {
        cksum = (cksum & 0xFFFF) + (cksum >> 16);
    }
   
    return ~cksum;
}
 
/**
 * @brief CheckSum16计算
 * @param pBuffer:数据缓存
 * @param len:数据长度
 * @return CheckSum16计算结果
*/ 
unsigned short CheckSum16(unsigned short *pBuffer, int len)
{
	unsigned short chksum;
	unsigned int sum = 0;

	while(len > 1)
	{
		sum += *pBuffer++;
		len -= 2;
	}
	
	if(len == 1)
		sum += *(unsigned char*)pBuffer;
		
	sum = (sum>>16) + (sum & 0xffff);
	sum += (sum>>16);
	chksum = ~sum;
	return (chksum);
}

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#ifndef __CHECKSUM_H__
#define __CHECKSUM_H__

/**
 * @brief CheckSum8计算
 * @param cksum : 计算结果初始值,一般为0
 * @param pBuffer : 数据缓存
 * @param size : 数据长度
 * @return CheckSum8计算结果
*/
unsigned short CheckSum8(unsigned int cksum, void *pBuffer,  int size);

/**
 * @brief CheckSum16计算
 * @param pBuffer:数据缓存
 * @param len:数据长度
 * @return CheckSum16计算结果
*/ 
unsigned short CheckSum16(unsigned short *pBuffer, int len);

#endif //__CHECKSUM_H__

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#include "stdio.h"
#include "stdlib.h"

#include "checksum.h"

unsigned char _data8 [] = {
    0x00, 0x00, // checksum result
    0x11, 0x12,
    0x13, 0x14,
    0x15, 0x14,
    0x00, 0x02,
    0x11, 0x12,
    0x13, 0x14,
    0x15, 0x14,
    0xff, 0x02,
    0x11, 0x12,
    0x13, 0x14,
    0xff, 0x14,
    0x11, 0x12,
    0x13, 0xcc,
    0x15, 0x14,
    0x00, 0x02,
    0x11, 0x12,
    0x13, 0x14,
    0x15, 0xdd,
    0x00, 0x02,
    0x11, 0x1f,
    0x13, 0x14,
    0x15, 0x14,
    0x11, 0x12,
    0x13, 0x14,
    0x15, 0x14,
    0x00, 0x02,
    0x11, 0x12,
    0x13, 0x14,
    0x19, 0x14,
    0x00, 0x02,
    0x11, 0x12,
    0xf3, 0x14,
    0xff
};

unsigned short _data16 [] = {
    0x0000, // checksum result
    0x1238,
    0x2039,
    0x2384,
    0xaf92,
    0x2848,
    0xbc38,
    0x2039,
    0x2384,
    0xaf92,
    0x2848,
    0x1238,
    0xa839,
    0xff84,
    0xaf92,
    0x2848
};

int main(int argc, char**argv)
{
    unsigned short chksum;
    printf("CheckSum8 demo.n");

    chksum = CheckSum8(0, _data8, sizeof(_data8));
    printf("CheckSum8 :0x%04xn", chksum);

    _data8[0] = chksum >> 8;
    _data8[1] = chksum & 0xff;
    //_data8[sizeof(_data8)-2] = chksum >> 8;
    //_data8[sizeof(_data8)-1] = chksum & 0xff;

    chksum = CheckSum8(0, _data8, sizeof(_data8));
    if (chksum != 0) {
        printf("CheckSum8 incorrect :0x%04x.n", chksum);
    } else {
        printf("CheckSum8 correct :0x%04x.n", chksum);
    }


    printf("nCheckSum16 demo.n");
    chksum = CheckSum16(_data16, sizeof(_data16));
    printf("CheckSum16:0x%04xn", chksum);
    _data16[0] = chksum;
    //_data16[sizeof(_data16)/sizeof(unsigned short) - 1] = chksum;
    chksum = CheckSum16(_data16, sizeof(_data16));
    if (chksum != 0) {
        printf("CheckSum16 incorrect :0x%04x.n", chksum);
    } else {
        printf("CheckSum16 correct :0x%04x.n", chksum);
    }
    
    return 0;
}