C++ 执行个函数，求帮助

[wangzhe1991919]

1.不懂C ,C++，求帮助
2.现有一段C++ 代码， 已知输入参数， 求结果
3.输入参数 16进制码， "30 31 30 31 32 39"
4.C++函数代码（CRC16校验）

unsigned int gen_crc(BYTE far *frame, short frame_len)
{
        BYTE c, treat, bcrc;
        unsigned int wcrc = 0;
        short i, j;

        for (i = 0; i < frame_len; i++)
        {
                c = frame[i];
                for (j = 0; j < 8; j++)
                {
                        treat = c & 0x80;
                        c <<= 1;
                        bcrc = (wcrc >> 8) & 0x80;
                        wcrc <<= 1;
                        if (treat != bcrc)
                                wcrc ^= 0x1021;
                }
        }
        return wcrc;
}

5.求个返回结果。
6.这种计算方式是对应的哪种类型？

[丁劲犇]

0x1021= 0001 0000 0010 0001, 即 x^12+x^5+1, 程序已经判断了最高位，因此，为 x^16 + x^12+x^5+1

这个程序其实就是做了二进制余二除法。

具体的意义，建议单步跟踪来看。

[丁劲犇]

#include <vector>
#include <stdio.h>
unsigned int gen_crc(const unsigned char *frame, short frame_len)
{
	unsigned char c, treat, bcrc;
	unsigned int wcrc = 0;
	short i, j;

	for (i = 0; i < frame_len; i++)
	{
		c = frame[i];
		for (j = 0; j < 8; j++)
		{
			treat = c & 0x80;
			c <<= 1;
			bcrc = (wcrc >> 8) & 0x80;
			wcrc <<= 1;
			if (treat != bcrc)
				wcrc ^= 0x1021;
		}
	}
	return wcrc;
}

unsigned int gen_crcbit(const unsigned char *frame, short frame_len)
{
	std::vector<unsigned char> vec_bits;
	for (int i=0;i<frame_len*8;++i)
		vec_bits.push_back((frame[i/8]>>(7-i%8))&0x01);
	for (int i=0;i<16;++i)
		vec_bits.push_back(0);
	const unsigned char poly[17] = {1,0,0,0,1,0,0,0,0,0,0,1,0,0,0,0,1};
	for (int j=0;j<vec_bits.size();++j)
		if (vec_bits[j])
			putchar('1');
		else
			putchar('0');

	for (int i=0;i<frame_len*8;++i)
	{
		if (vec_bits[i])
		{
			for (int j=0;j<17;++j)
				vec_bits[i+j] = vec_bits[i+j]==poly[j]?0:1;
		}
		else
			continue;

		printf("\n");
		for (int j=0;j<i;++j)
			putchar(' ');
		for (int j=0;j<17;++j)
			putchar(poly[j]==0?'0':'1');

		printf("\n");


		bool bhit1 = false;

		for (int j=0;j<frame_len*8+16;++j)
			if (vec_bits[j])
			{
				putchar('1');
				bhit1 = true;
			}
			else if (bhit1)
				putchar('0');
			else
				putchar(' ');

	}
	int cc = 0;
	for (int j=0;j<16;++j)
	{
		cc<<=1;
		cc += vec_bits[frame_len*8+j];
	}

	return cc;
}

int main(int argc, char *argv[])
{
	const unsigned char pp[] = {0x30,0x31,0x30,0x31,0x32,0x39};

	unsigned int crc1 = gen_crcbit(pp,6);

	printf ("\n%04x\n",crc1);

	crc1 = gen_crc(pp,6);

	printf ("\n%04x\n",crc1 & 0x0ffff);
	return 0;
}

输出：

0011000000110001001100000011000100110010001110010000000000000000
  10001000000100001
   1001000110101000100000011000100110010001110010000000000000000
   10001000000100001
      1100110111000000000011000100110010001110010000000000000000
      10001000000100001
       100010111010000100011000100110010001110010000000000000000
       10001000000100001
             111011000110011000100110010001110010000000000000000
             10001000000100001
              11001000111011010100110010001110010000000000000000
              10001000000100001
               1000000111111011100110010001110010000000000000000
               10001000000100001
                   100111101011000110010001110010000000000000000
                   10001000000100001
                      101101010000100010001110010000000000000000
                      10001000000100001
                        1111010001100000001110010000000000000000
                        10001000000100001
                         111110001110000101110010000000000000000
                         10001000000100001
                          11100001111000111110010000000000000000
                          10001000000100001
                           1101001111100110110010000000000000000
                           10001000000100001
                            101101111110110010010000000000000000
                            10001000000100001
                              1111111111110000010000000000000000
                              10001000000100001
                               111011111100000110000000000000000
                               10001000000100001
                                11001111101000100000000000000000
                                10001000000100001
                                 1000111101100101000000000000000
                                 10001000000100001
                                      11101110101100000000000000
                                      10001000000100001
                                       1100110101000001000000000
                                       10001000000100001
                                        100010101010001100000000
                                        10001000000100001
                                              101011001110000000
                                              10001000000100001
                                                1001001111000010
93c2

93c2

[wangzhe1991919]

那就是对应了这种算法，