Nand2Tetris week-4

作业说明

作业网站

循环 LOOP

Mult

The program assumes that R0>=0, R1>=0, and R0*R1<32768. Your program need not test these conditions, but rather assume that they hold.

本题在课程网站的作业说明中，明确给出了两个输入寄存器的值非负，简化了许多。

乘法就是多次加法，根据给的LOOP代码进行修改即可。

测试时需要先进行汇编，生成hack文件

提交时需要修改文件名，首字母大写

// This file is part of www.nand2tetris.org
// and the book "The Elements of Computing Systems"
// by Nisan and Schocken, MIT Press.
// File name: projects/04/Mult.asm
// Multiplies R0 and R1 and stores the result in R2.
// (R0, R1, R2 refer to RAM[0], RAM[1], and RAM[2], respectively.)
// Put your code here.
@R0
D=M
@n
M=D // n = [R0]
@i 
M=0 // i = 0 for(i=0; i < n; ++ i)
@sum 
M=0 // sum = 0
(LOOP)
    @i
    D=M
    @n
    D=D-M
    @STOP 
    D;JEQ // if i > n goto STOP
    @sum
    D=M
    @R1
    D=D+M
    @sum
    M=D // sum = sum + [R1]
    @i
    M=M+1 // i = i + 1
    @LOOP
    0;JMP
(STOP)
    @sum
    D=M
    @R2
    M=D // RAM[1] = sum
(END)
    @END 
    0;JMP

Fill

伪代码：外循环永真，根据键盘是否输入遍历一遍屏幕，输出颜色。

int start = screen.start, end = screen.end;
while(true) {
    if(keyborad is not pressed) {
        for(int i = start; i < end; ++ i) {
            //print white
        }
    } else {
        for(int i = start; i < end; ++ i) {
            //print black
        }
    }
}

测试前仍旧需要先汇编为hack文件，导入FillAutomatic.tst进行测试。

// This file is part of www.nand2tetris.org
// and the book "The Elements of Computing Systems"
// by Nisan and Schocken, MIT Press.
// File name: projects/04/Fill.asm

// Runs an infinite loop that listens to the keyboard input.
// When a key is pressed (any key), the program blackens the screen,
// i.e. writes "black" in every pixel;
// the screen should remain fully black as long as the key is pressed. 
// When no key is pressed, the program clears the screen, i.e. writes
// "white" in every pixel;
// the screen should remain fully clear as long as no key is pressed.

// Put your code here.

//note: write 2-layer loops 
//the first loop is while(true) to chack if any key is push
//the second loop is for(int i=0; i < screen.size(); ++ i) 
//this loop print white or black on screen.
//8192, 8K, the screen size

@8192
D=A
@end
M=D

(LOOP)
    @SCREEN
    D=A
    @addr       //base address
    M=D

    @i
    M=0

    @KBD
    D=M         //cheack the keyboard

    @WHITE
    D; JEQ        
    @BLACK
    D; JNE

(WHITE)
    @end
    D=M
    @i
    D=D-M       //if(end-i == 0) break into first loop 
    @LOOP
    D;JEQ    

    @addr
    A=M
    M=0            //print 0

    @i
    M=M+1        //i++

    @addr
    M=M+1

    @WHITE
    0;JMP


(BLACK)
    @end
    D=M
    @i
    D=D-M //if(end-i == 0) break into first loop 
    @LOOP
    D;JEQ    

    @addr
    A=M
    M=-1        //print -1

    @i
    M=M+1        //i++

    @addr
    M=M+1

    @BLACK
    0;JMP

作业提交

总结

本周作业更接近平时写的高级语言程序设计，相对上一周来说简单些。但需要直接操作寄存器，有些感觉应该一下子写好的东西，费了好久才能写出来。DEBUG也不是很容易。

视频有些长，看了一半就忘了一些，写的时候也就不熟练，难构思。也因此懈怠了，希望能保持每天学一点的节奏，更充实。