/* Follow is the introducation for the file in Chinese.
* 版權(quán)和版本聲明中文模式
* 
* 文件名稱：sum_check.c
* 文件標(biāo)識(shí)：xx.yy.zz 參見配置管理計(jì)劃書
* 摘    要：定義校驗(yàn)和相關(guān)函數(shù)
* 
*/

#include "sum_check.h"

//-----------------------------------------------------------------------------
// compute the data sum,and return the sum's patch-code(not a professiona glossary)
// the function only use in functions append_sum_check and verify_sum_check_ok
// so the function is a local function.
//-----------------------------------------------------------------------------
/*
* Function name		: compute_sum_check
* Function describe	: compute the datas sum result and the sum's patch-code
*					   
* Input				: p:the datas point 
*						: length:the data length,length < 0xff
* Output 				: the sum's patch-code
* Ram be effected		: none
* global variable		: none
* Called module		: none
*			
*/
unsigned char compute_sum_check(unsigned char xdata *p,unsigned char length)
{
	unsigned char sum,i;
	
	sum = 0;
	for(i=0;i<length;i++)
	{
		sum += *(p+i);
	}
	sum = 0x100-sum;
	return sum;
}

/*
* Function name		: append_sum_check
* Function describe	: append the sum-check's patch-code follow the datas
*
* Input				: p:the datas point 
*						: length:the data length,length < 0xff
* Output 				: none
* Ram be effected		: none
* global variable		: none
* Called module		: compute_sum_check
*
*/
void append_sum_check(unsigned char xdata *p,unsigned char length)
{
	*(p + length) = compute_sum_check(p,length);
}


/*
* Function name		: verify_sum_check_ok
* Function describe	: verify the datas's sum-check are correct
*
* Input				: p:the datas point 
*						: length:the data length,length <= 0xff
* Output 				: SUM_CORRECT:	the datas sum check result are correct.
* SUM_INCORRECT		:the datas sum check result are false.
* global variable		: none
* Called module		: compute_sum_check
*
*/
#define SUM_CORRECT	1
#define SUM_INCORRECT	0
bit verify_sum_check_ok(unsigned char xdata *p,unsigned char length)
{
	if(compute_sum_check(p,length) == 0x00)
	{
		return	SUM_CORRECT;
	}
	else
	{
		return SUM_INCORRECT;
	}
}