cpu大小端測試

關於cpu大小端中int或short的存放順序，以及大小端序到網絡序的轉換

測試如下：

#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，通過ntohl轉換爲網絡字節序時數據沒有變化


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，通過ntohl轉換爲網絡字節序時數據高低變換

也就是說，大端的系統上ntoh相關函數是不作處理的

小端的系統htoh相關函數會將高低位變換