大数减法之无符号减法

wangarc

昨天写了完成了加法，改一改完成减法。
本段测试程序是人肉直接输入参数。也可以用以下函数获得：
判断字符串是否为一个有效的数

本段程序需要调用以下函数：
两个十进制字符相减得到十进制字符的结果和借位

[C] 纯文本查看 复制代码

int sub_ip_dp(char * str1, int dot_pos1, int i_qty1, int d_qty1,
			  char * str2, int dot_pos2, int i_qty2, int d_qty2,
			  char * str3, int str3_array_size, int * offset);
/*  sub_ip_dp() return 1 if no error, -1 if sub error (str1 < str2), 0 if other errors.
 *  sub integral part and decimal part (str3 = str1 - str2)
 *  dot_pos: index of str where '.' located for decimal number
 *							or '\0' located for integral number.
 *	i_qty: integral number quantity (integral part length)
 *	d_qty: decimal number quantity (decimal part length)
 *	str3: array to store result
 *	str3_array_size: array size
 *	offset: result will start from here (this function write result from tail to head)
 */

int main(void) //testing
{
	char * s1 = "0";
	char * s2 = "99999999999999999999";
	char * s3 = ".00000000000000000001";
	char * s4 = "1.00";
	char * s5 = "3.14159";
	char * s6 = "0003.14159000";
	char * s7 = "9999999999.9999999999";
	char str[128];
	int i, r;
	
	r = sub_ip_dp(s1, 1, 1, 0, s2, 20, 20, 0, str, 128, &i);
	if (r == 1) 
		printf("\nreturn %d, offset = %d,\n%s - %s = %s\n", r, i, s1, s2, str + i);
	else {
		r = sub_ip_dp(s2, 20, 20, 0, s1, 1, 1, 0, str, 128, &i);
		printf("\nreturn %d, offset = %d,\n%s - %s = -%s\n", r, i, s1, s2, str + i);
		}
	r = sub_ip_dp(s2, 20, 20, 0, s3, 0, 0, 20, str, 128, &i);
	if (r == 1)
		printf("\nreturn %d, offset = %d,\n%s - %s = %s\n", r, i, s2, s3, str + i);
	else {
		r = sub_ip_dp(s3, 0, 0, 20, s2, 20, 20, 0, str, 128, &i);
		printf("\nreturn %d, offset = %d,\n%s - %s = -%s\n", r, i, s2, s3, str + i);
		}
	r = sub_ip_dp(s3, 0, 0, 20, s4, 1, 1, 2, str, 128, &i);
	if (r == 1)
		printf("\nreturn %d, offset = %d,\n%s - %s = %s\n", r, i, s3, s4, str + i);
	else {
		r = sub_ip_dp(s4, 1, 1, 2, s3, 0, 0, 20, str, 128, &i);
		printf("\nreturn %d, offset = %d,\n%s - %s = -%s\n", r, i, s3, s4, str + i);
		}
	r = sub_ip_dp(s4, 1, 1, 2, s5, 1, 1, 5, str, 128, &i);
	if (r == 1) 
		printf("\nreturn %d, offset = %d,\n%s - %s = %s\n", r, i, s4, s5, str + i);
	else {
		r = sub_ip_dp(s5, 1, 1, 5, s4, 1, 1, 2, str, 128, &i);
		printf("\nreturn %d, offset = %d,\n%s - %s = -%s\n", r, i, s4, s5, str + i);
		}
	r = sub_ip_dp(s5, 1, 1, 5, s6, 4, 4, 8, str, 128, &i);
	if (r == 1) 
		printf("\nreturn %d, offset = %d,\n%s - %s = %s\n", r, i, s5, s6, str + i);
	else {
		r = sub_ip_dp(s6, 4, 4, 8, s5, 1, 1, 5, str, 128, &i);
		printf("\nreturn %d, offset = %d,\n%s - %s = -%s\n", r, i, s5, s6, str + i);
		}
	r = sub_ip_dp(s6, 4, 4, 8, s7, 10, 10, 10, str, 128, &i);
	if (r == 1) 
		printf("\nreturn %d, offset = %d,\n%s - %s = %s\n", r, i, s6, s7, str + i);
	else {
		r = sub_ip_dp(s7, 10, 10, 10, s6, 4, 4, 8, str, 128, &i);
		printf("\nreturn %d, offset = %d,\n%s - %s = -%s\n", r, i, s6, s7, str + i);
		}
	
	return 0;
}

int sub_ip_dp(char * str1, int dot_pos1, int i_qty1, int d_qty1,
			  char * str2, int dot_pos2, int i_qty2, int d_qty2,
			  char * str3, int str3_array_size, int * offset)
{
	//return 1 if no error, -1 if sub error (str1 < str2), 0 if other errors.
	char * p1 = str1 + dot_pos1;	// p1 is a pointer to '.' or '\0' of str1
	char * p2 = str2 + dot_pos2;	// p2 is a pointer to '.' or '\0' of str2
	int i = str3_array_size;		// i is an index of str3, copy to *offset finally
	char borrow = '0';				// borrow is a borrow
	char c1, c2, c3;				// c1, c2 and c3 are temp chars
	int k, j;						// k and j are temp index
	
	// set '\0' at the end of str3
	if (--i >= 0)
		str3[i] = '\0';
	else
		return 0;	//Error: insufficient space in str3

	// sub decimal part: from tail to head
	k = (d_qty1 > d_qty2) ? d_qty1 : d_qty2;
	while (k > 0)
	{
		c1 = (k > d_qty1) ? '0' : p1[k];
		c2 = (k > d_qty2) ? '0' : p2[k];
		if (0 == dec_char_sub(borrow, c1, c2, &borrow, &c3))
			return 0;		//Error: return error from dec_char_add()
		
		if (--i >= 0)
			str3[i] = c3;
		else
			return 0;		//Error: insufficient space in str3
		
		if (str3[i+1] == '\0' && str3[i] == '0')
			i++;			//ignore '0' in the end of decimal
		
		--k;
	}
	
	// put a '.' in the string
	if (str3[i] != '\0')
	{
		if (--i >= 0)
			str3[i] = '.';
		else
			return 0;		//Error: insufficient space in str3
	}

	// sub integral part: from tail to head
	k = 1;
	j = (i_qty1 > i_qty2) ? i_qty1 : i_qty2;
	while (k <= j)
	{
		c1 = (k > i_qty1) ? '0' : p1[-k];
		c2 = (k > i_qty2) ? '0' : p2[-k];
		if (0 == dec_char_sub(borrow, c1, c2, &borrow, &c3))
			return 0;		//Error: return error from dec_char_add()
		
		if (--i >= 0)
			str3[i] = c3;
		else
			return 0;		//Error: insufficient space in str3
		
		++k;
	}

	// consider borrow after last dec_char_sub()
	if (borrow == '1')
		return -1;		//Error: str1 is smaller than str2, it's not allowed
						//you should switch str1 and str2
						//try again: - (str2 - str1)

	// ignore all begining '0' in the string
	while (str3[i] == '0')
		++i;

	// add a '0' if start with a '.'
	if (str3[i] == '.')
	{
		if (--i >= 0)
			str3[i] = '0';
		else
			return 0;		//Error: insufficient space in str3
	}

	// add a '0' if empty string
	if (str3[i] == '\0')
	{
		if (--i >= 0)
			str3[i] = '0';
		else
			return 0;		//Error: insufficient space in str3
	}

	// set *offset for str3
	*offset = i;
	return 1;	//Done
}

ghimi

写的不错，学习了