learn mips

可以使用MARS来编汇编,MARS是一个用java编的IDE,它是一个模拟环境.

样例:重要的句子输出三遍

.data
   str: .asciiz "weidiao is great\n"
.text
j main
f:
   la $a0,str
   li $v0,
   syscall
   jr $ra
main:
   li $t1,
   li $t2,3
loop:
   bgt $t1,$t2,over
   addi $t1,$t1,
   jal f
   j loop

   syscall

指令文档:链接

下面程序为一个四则运算程序,学习汇编就是要大量的阅读实例.实例学习在编程技术中至关重要.

    #simple example :a small calculater’
    .text                       # text section
    .globl main                 # call main by SPIM
    main:
        la $t0, value
        #t0 is the address of the value
                  # load address "value" into $t0
        la $a0,msg0
        li $v0,4
        syscall             #print "please choose the operation:"  

        li  $v0, 5
        syscall
        sw  $v0, 8($t0)  #operation is stored to t0+8---the second byte

        la $a0,msg1  #v0 controls the syscall.a0 controls the output_data;
        li $v0,4
        syscall             #print "first num:"  

        li  $v0, 5    #load integer 5 to v0,this is the read operation.
        syscall
        sw  $v0, 0($t0)  #store $v0

        la $a0,msg2
        li $v0,4
        syscall             #print " second num:"  

        li  $v0, 5
        syscall
        sw  $v0, 4($t0)         #read the other num   

        la $a0,newline
        li $v0,4
        syscall             #print "/n"  

        lw $t1, 0($t0)          # load the first num
        lw $t2, 4($t0)          # load the second num
        lw $t3, 8($t0)          # load the operation  

        beq $t3,1,addOp         # if +
        beq $t3,2,subOp         # if -
        beq $t3,3,mulOp         # if *
        beq $t3,4,divOp         # if /  

    addOp:
        add $t4, $t1, $t2       # $t1 + $t2 = $t4
        sw $t4, 12($t0)         #
        la $t5,addFlag
        j printResult
    subOp:
        sub $t4, $t1, $t2       # $t1 - $t2 = $t4
        sw $t4, 12($t0)
        la $t5,subFlag
        j printResult
    mulOp:
        mul $t4, $t1, $t2       # $t1 * $t2 = $t4
        sw $t4, 12($t0)
        la $t5,mulFlag
        j printResult
    divOp:
        div $t4, $t1, $t2       # $t1 / $t2 = $t4
        sw $t4, 12($t0)
        la $t5,divFlag
        j printResult  

    printResult:
        lw $a0,0($t0)
        li $v0,1
        syscall             #read first number  

        la $a0,0($t5)
        li $v0,4
        syscall             #print opflag  

        lw $a0,4($t0)
        li $v0,1
        syscall             #print second number  

        la $a0,equalStr
        li $v0,4
        syscall             #print " = "  

        lw $a0,12($t0)
        li $v0,1
        syscall             # print sum result
        j exit  

    exit:
        la $a0,newline
        li $v0,4
        syscall             #print " /n "  

        li $v0,10
        syscall             # exit
    # data section
    .data
    value:  .word 0, 0, 0 ,0 ,0     # 0: first num ,4 : second num , 8 : operation , 12:result
    msg0        :   .asciiz " please choose the operation(1~4):/n/t/t1 : +,addition /n/t/t2 : -,subtracter/n/t/t3 : * multiplication /n/t/t4 : /,division/n"
    msg1        :   .asciiz "first num:"
    msg2        :   .asciiz "second num:"
    addFlag     :   .asciiz " + "
    subFlag     :   .asciiz " - "
    mulFlag     :   .asciiz " * "
    divFlag     :   .asciiz " / "
    equalStr    :   .asciiz " = "
    newline     :   .asciiz "/n===============================/n"   

样例:打印九九乘法表

.data
  op :.asciiz "*"
  eq:.asciiz "="
  line:.asciiz "\n"
  space:.asciiz " "
.text
  j main
  print:
    move $a0,$t1
    li $v0,
    syscall

    la $a0,op
    li $v0,
    syscall

    move $a0,$t2
    li $v0,
    syscall

    la $a0,eq
    li $v0,
    syscall

    mult $t1,$t2
    mflo $a0
    li $v0,
    syscall

    la $a0,space
    li $v0,
    syscall

    blt $t2,$t1,ret
    la $a0,line
    syscall

    ret:
    jr $ra
  main:
    li $t1,
    for1:
      addi $t1,$t1,
      bgt $t1,,for1_out
      li $t2,
      for2:
        addi $t2,$t2,
        bgt $t2,$t1,for1
        jal print
        j for2
      j for1
    for1_out:
      li $v0,
      syscall