第一次互评作业：MIPS汇编程序设计

第一题：用系统功能调用实现简单输入输出

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，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，

(4) 支持反复输入，直到按“?”键结束程序。

.data
u_word:     .asciiz
"Alpha ","Bravo ","China ","Delta ","Echo ","Foxtrot ",
"Golf ","Hotel ","India ","Juliet ","Kilo ","Lima ",
"Mary ","November ","Oscar ","Paper ","Quebec ","Research ",
"Sierra ","Tango ","Uniform ","Victor ","Whisky ","X-ray ",
"Yankee ","Zulu "
uw_offset:  .word
0,7,14,21,28,34,43,49,56,63,71,
77,83,89,99,106,113,121,131,
139,146,155,163,171,178,186
l_word:     .asciiz
"alpha ","bravo ","china ","delta ","echo ","foxtrot ",
"golf ","hotel ","india ","juliet ","kilo ","lima ",
"mary ","november ","oscar ","paper ","quebec ","research ",
"sierra ","tango ","uniform ","victor ","whisky ","x-ray ",
"yankee ","zulu "
lw_offset:  .word
0,7,14,21,28,34,43,49,56,63,71,
77,83,89,99,106,113,121,131,
139,146,155,163,171,178,186
number:     .asciiz
"zero ", "First ", "Second ", "Third ", "Fourth ",
"Fifth ", "Sixth ", "Seventh ","Eighth ","Ninth "
n_offset:   .word
0,6,13,21,28,36,43,50,59,67

.text
.globl main
main:       li $v0, 12 # read character
syscall
sub $t1, $v0, 63 # '?'
beqz $t1, exit
sub $t1, $v0, 48 # '0'
slt $s0, $t1, $0 # if t1 < 0 then s0 = 1
bnez $s0, others

# is number?
sub $t2, $t1, 10 # number
slt $s1, $t2, $0 # if t2 < 0 then s1 = 1
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, getuword

# 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, getlword
j others

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

# upper case word
getuword:   sub $t3, $t3, 1
sll $t3, $t3, 2
la $s0, uw_offset
add $s0, $s0, $t3
lw $s1, ($s0)
la $a0, u_word
add $a0, $s1, $a0
li $v0, 4
syscall
j main

# lower case word
getlword:   sub $t3, $t3, 1
sll $t3, $t3, 2
la $s0, lw_offset
add $s0, $s0, $t3
lw $s1, ($s0)
la $a0, l_word
add $a0, $s1, $a0
li $v0, 4
syscall
j main

others:     and $a0, $0, $0
add $a0, $a0, 42 # '*'
li $v0, 11 # print character
syscall
j main

exit:       li $v0, 10 # exit
syscall

第二题：字符串查找比较

利用系统功能调用从键盘输入一个字符串，然后输入单个字符，查找该字符串中是否有该字符（区分大小写）。具体要求如下：

(1) 如果找到，则在屏幕上显示：

Success! Location: X

其中，X为该字符在字符串中第一次出现的位置

(2) 如果没找到，则在屏幕上显示：

Fail!

(3) 输入一个字符串后，可以反复输入希望查询的字符，直到按“?”键结束程序

(4) 每个输入字符独占一行，输出查找结果独占一行，位置编码从1开始。

提示：为避免歧义，字符串内不包含"?"符号

格式示例如下：

abcdefgh

a

Success! Location: 1

x

Fail!

.data
msg_s:      .asciiz "\r\nSuccess! Location: "
msg_f:      .asciiz "\r\nFail!\r\n"
s_end:      .asciiz "\r\n"
buf:        .space 100

.text
.globl main
main:       la $a0, buf # address of input buffer
la $a1, 100 # maximum number of characters to read
li $v0, 8 # read string
syscall

inputchar:  li $v0, 12 # read character
syscall
addi $t7, $0, 63 # '?'
sub $t6, $t7, $v0
beq $t6, $0, exit
add $t0, $0, $0
la $s1, buf

find_loop:  lb $s0, 0($s1)
sub $t1, $v0, $s0
beq $t1, $0, success
addi $t0, $t0, 1
slt $t3, $t0, $a1
beq $t3, $0, fail
addi $s1 $s1, 1
j find_loop

success:    la $a0, msg_s
li $v0, 4 # print string
syscall
addi $a0, $t0, 1
li $v0, 1 # print integer
syscall
la $a0, s_end
li $v0, 4
syscall
j inputchar

fail:       la $a0, msg_f
li $v0, 4
syscall
j inputchar

exit:       li $v0, 10
syscall