MIPS:用系统功能调用实现简单输入输出

实验目的：熟悉MIPS的指令，掌握简单的汇编程序结构。
实验内容：利用系统功能调用从键盘输入，转换后在屏幕上显示，具体要求如下：
(1) 如果输入的是字母（A~Z，不区分大小写）或数字（0~9），则将其转换成对应的英文单词后在屏幕上显示，对应关系见下表
(2) 若输入的不是字母或数字，则在屏幕上输出字符“*”
(3) 每输入一个字符，即时转换并在屏幕上显示，需考虑显示结果的清晰美观
(4) 支持反复输入，直到按？键结束程序
(5) 程序结束时，在屏幕上显示本人的姓名全拼和学号
例：在键盘上输入“PKU2011/”，对应输出内容为“Papa Kilo Uniform two zero one one *”

A	Alpha	N	November	1	one
B	Bravo	O	Oscar	2	two
C	Charlie	P	Papa	3	three
D	Delta	Q	Quebec	4	four
E	Echo	R	Romeo	5	five
F	Foxtrot	S	Sierra	6	six
G	Golf	T	Tango	7	seven
H	Hotel	U	Uniform	8	eight
I	India	V	Victor	9	nine
J	Juliet	W	Whisky	0	zero
K	Kilo	X	X-ray
L	Lima	Y	Yankee
M	Mike	Z	Zulu

.data
alphabet: .asciiz "Alpha ","Bravo ","Charlie ","Delta ","Echo ","Foxtrot ","Golf ","Hotel ","India ","Juliet ","Kilo ","Lima ","Mike ","November ","Oscar ","Papa ","Quebec ","Romeo ","Sierra ","Tango ","Uniform ","Victor ","Whisky ","X-ray ","Yankee ","Zulu "
al_offset: .word 0,7,14,23,30,36,45,51,58,65,73,79,85,91,101,108,114,122,129,137,144,153,161,169,176,184
number: .asciiz "zero ", "one ", "two ", "three ", "four ", "five ", "six ", "seven ","eight ","nine "
n_offset: .word 0,6,11,16,23,29,35,40,47,54
myname:	.asciiz "\r\nNAME: Wu Yiting\r\n"
myid:	.asciiz "ID: 1200012875\r\n"

.text
.globl main
#? word length[] = 4
main:	li $v0, 12
syscall
sub $t1, $v0, 63	# is '?" ?
beqz $t1, exit
sub $t1, $v0, 48 	# 0 ascii
slt $s0, $t1, $0	# if t1 < 0 then s0 = 1
bnez $s0, others

sub $t2, $t1, 10
slt $s1, $t2, $0
bnez $s1, getnum

# is capital?
sub $t2, $v0, 91
slt $s3, $t2, $0	# if v0 <= 'Z' then s3 = 1
sub $t3, $v0, 64
sgt $s4, $t3, $0	# if v0 >='A' then s4 = 1
and $s0, $s3, $s4	# if s3 == 1 && s4 == 1
bnez $s0, getword

# is lower case?
sub $t2, $v0, 123
slt $s3, $t2, $0	# if v0 <= 'z' then s3 = 1
sub $t3,$v0, 96
sgt $s4, $t3, $0	# if v0 >= 'a' then s4 = 1
and $s0, $s3, $s4
bnez $s0, getword
j others

getnum: add $t2, $t2, 10
sll $t2, $t2, 2
la $s0, n_offset
add $s0, $s0, $t2
lw $s1, ($s0)
#sll $s1, $s1, 1
la $a0, number
add $a0, $a0, $s1
li $v0, 4
syscall
j main

getword:sub $t3, $t3, 1
sll $t3, $t3,2
la $s0, al_offset
add $s0, $s0, $t3
lw $s1, ($s0)
#sll $s1, $s1, 1
la $a0, alphabet
add $a0, $s1, $a0
li $v0, 4
syscall
j main

others:	and $a0, $0, $0
add $a0, $a0, 42
li $v0, 11
syscall
j main

exit:	la $a0, myname
li $v0, 4
syscall
la $a0, myid
li $v0, 4
syscall
li $v0, 1
syscall

##problem of offset

1、跟x86这题类似采用了二次寻址的思想（偏移量是写代码跑出来的=v=, 机器可以做的事情还是懒得数了）

2、夹逼确定数字以及大小写

3、注意.word偏移量*4（这里‘，’不会影响），而.ascii偏移量*1（尤其坑的是‘，’也算一位，调了很久才发现）