C/C++中解析CAN总线信号：从原始字节提取比特位

#include <iostream>
#include <array>
#include <cstring>
#include <cstdlib>

// 位操作辅助宏
#define BITSET(p,n)  ((p) |= (1u <<(n)))
#define BITCLR(p,n)  ((p) &= ~(1u <<(n)))
#define BITGET(i,n)  ((i) & (1u << (n)))

// 定义用于截取高位和低位边缘部分的掩码
unsigned char msbmask[] = {
	0xFF, 0xFE, 0xFC, 0xF8,
	0xF0, 0xE0, 0xC0, 0x80
};
unsigned char lsbmask[] = {
	0x01, 0x03, 0x07, 0x0F,
	0x1F, 0x3F, 0x7F, 0xFF
};

// 用于存储待解析信号的位置信息
// MSBPos: 信号最高位在报文总比特流中的索引（0开始）
// LSBPos: 信号最低位在报文总比特流中的索引
typedef struct {
	unsigned char* can_data_ptr;
	int len;
	int msb_pos;
	int lsb_pos;
}can_signal;

static can_signal cansingal;

// 初始化信号数据
can_data_assignment(unsigned char* candata, int msbpos, int lsbpos, int lens)
{
	cansingal.can_data_ptr = (unsigned char*)malloc(lens);
	memcpy((void *)cansingal.can_data_ptr, (const void *)candata,lens);
	cansingal.len = lens;
	cansingal.msb_pos = msbpos;
	cansingal.lsb_pos = lsbpos;
	return 0;
 }

// 执行信号提取
unsigned int can_data_transfer_signal()
{
	// a,b 计算当前所在字节及字节内偏移
	int a = 0;
	int b = 0;
	int c = 0;
	int d = 0;
	unsigned int singal = 0;
	
	printf("%d %d\n", cansingal.lsb_pos, cansingal.msb_pos);
	printf("%02x %02x %02x %02x\n", cansingal.can_data_ptr[0], cansingal.can_data_ptr[1], cansingal.can_data_ptr[2], cansingal.can_data_ptr[3]);
	
	a = cansingal.lsb_pos / 8; // 所在字节
	b = cansingal.lsb_pos % 8; // 字节内最低位偏移
	
	cansingal.can_data_ptr[a] = cansingal.can_data_ptr[a] & msbmask[b]; 
	
	c = cansingal.msb_pos / 8;
	d = cansingal.msb_pos % 8; 
	
	cansingal.can_data_ptr[c] = cansingal.can_data_ptr[c] & lsbmask[d]; 
	
	printf("%02x %02x %02x %02x\n", cansingal.can_data_ptr[0], cansingal.can_data_ptr[1], cansingal.can_data_ptr[2], cansingal.can_data_ptr[3]);
	
	// 逐位提取并重组目标信号
	for (int i = cansingal.lsb_pos, j = 0; i <= cansingal.msb_pos; ++i, ++j)
	{
		a = i / 8;
		b = i % 8;
		if ( BITGET(cansingal.can_data_ptr[a], b) )
		{
			BITSET(singal, j);
		}
		else
		{
			BITCLR(singal,j);
		}
	}
	return singal;
}

// 释放资源
void can_data_free(void)
{
	free(cansingal.can_data_ptr);
	cansingal.len = 0;
	cansingal.lsb_pos = 0;
	cansingal.msb_pos = 0;
}

int main(int argc, char* argv[])
{
	// 测试用例：4字节报文
	unsigned char candata[4] = { 0x44, 0xFE, 0x23, 0x81};
	
	// 模拟提取：从第14位到第31位的信号
	can_data_assignment(candata, 31, 14, 4); 
	unsigned int c = can_data_transfer_signal();
	can_data_free();
	
	printf("Signal Value: %d\n", c);
	return 0;
}

#include <stdio.h>
int main(int argc, char *argv[]){
    int a[] = {1, 3, 5, 7, 9};
    int *p, i;
    p = a;
    printf("%p %p %p\n", a, a+1, a+2);
    for(i = 0; i < 5; i++){
        printf("%d %d %d %d\n", a[i], *(p+i), *(a+i), p[i]);
    }
    return 0;
}