计算机底层编译原理 二进制

Posted 2020-10-02 Mr_Kenson

import java.io.IOException;

public class Demo07 {

    public static void main(String[] args) 
        throws IOException{
        //int c = ‘中‘;
        int c = 0x4e2d;
        System.out.println(c);
        System.out.println(Integer.toBinaryString(c));  
        int m = 0x3f;
        //将c的最后6位截取下来为k
        int k = c&m;
        System.out.println(Integer.toBinaryString(k));
        //将字符c的编为UTF-8，得到最后一个字节b3
        int b3 = c&0x3f|0x80; 
        System.out.println(Integer.toBinaryString(b3));
        //编码b2
        int b2 = (c>>>6)&0x3f|0x80;
        System.out.println(Integer.toBinaryString(b2));
        //编码b1
        int b1 = (c>>>12)|0xe0;
        //验证：
        byte[] bytes = {(byte)b1,(byte)b2,(byte)b3};
        String str = new String(bytes, "UTF-8");
        System.out.println(str);//中
        char cc = decodeUtf8(bytes);
        System.out.println(cc);
    }
    
    public static char decodeUtf8(byte[] bytes){
        int b1 = bytes[0];
        int b2 = bytes[1];
        int b3 = bytes[2];
        System.out.println(Integer.toBinaryString(b1));
        //b1 = 11111111 11111111 11111111 11100010 
        //b2 = 11111111 11111111 11111111 10111000
        //b3 = 11111111 11111111 11111111 10101101
        
// (b1&0xf)<<12 00000000 00000000 00100000 00000000
// (b2&0x3f)<<6 00000000 00000000 00001110 00000000
// (b3&0x3f)    00000000 00000000 00000000 00101101
        
        // ch=  00000000 00000000 00101110 00101101
        
        int ch = ((b1&0xf)<<12)|((b2&0x3f)<<6)|(b3&0x3f);
        return (char)ch;
    }

    public static byte[] utf8(char ch){
        int b1 = (ch>>>12)|0xe0;
        int b2 = (ch>>>6) & 0x3f | 0x80;
        int b3 = ch & 0x3f | 0x80;
        return new byte[]{(byte)b1,(byte)b2,(byte)b3};
    }    
}