cpu大小端测试

关于cpu大小端中int或short的存放顺序，以及大小端序到网络序的转换

测试如下：

#include <stdio.h>
#include <arpa/inet.h>

int main()
{
	unsigned int a = 0x12345678;
	unsigned int b;
	unsigned char *c;
	unsigned char *d;

	b = ntohl(a);

	c = (unsigned char *)&a;
	d = (unsigned char *)&b;

	printf("a = 0x%x, b = 0x%x\n", a, b);
	printf("c0 = 0x%x, c1 = 0x%x, c2 = 0x%x, c3 = 0x%x\n", c[0],c[1],c[2],c[3]);
	printf("d0 = 0x%x, d1 = 0x%x, d2 = 0x%x, d3 = 0x%x\n", d[0],d[1],d[2],d[3]);

	return 0;
}

大端mips

a = 0x12345678, b = 0x12345678
c0 = 0x12, c1 = 0x34, c2 = 0x56, c3 =0x78
d0 = 0x12, d1 = 0x34, d2 = 0x56, d3 =0x78

由此，大端的高位在低地址，通过ntohl转换为网络字节序时数据没有变化


小端arm：

a = 0x12345678, b = 0x78563412
c0 = 0x78, c1 = 0x56, c2 = 0x34, c3 = 0x12
d0 = 0x12, d1 = 0x34, d2 = 0x56, d3 = 0x78

由此，小端的低位在高地址，通过ntohl转换为网络字节序时数据高低变换

也就是说，大端的系统上ntoh相关函数是不作处理的

小端的系统htoh相关函数会将高低位变换