Question

How would we write a method to sort an array in Assembly, the array is defined in the main method and has 10 elements

Answer 1

Before going through the sorting process ,Let us understand the basic structure in MIPS Assembly language programming, with comparison, with our basic C++ programming language, so that you can get the basic idea of the MIPS assembly program

.data                      // #include<iostream.h>

.text                      # using namespace std;

main:                  # int main()

li $v0, 10            # return 0;

syscall

.data

myArray : .space        40       ^{_{// size of array is 40 , because 1 int = 4 bytes (Therefore 10 integers = 40 bytes}}

prompt    :      .asciiz    "Please enter 10 elements in an myArray" ^{_{// just a print message for the user}}

.text

.main :

#At start all registers will hold Zero value, Here Below is the declaration of all the #constants that we will use in the coding

• addi    $t0   ,   $t0   , 40   # command for add, it works as $t0 = $t0 +40, Here it is used to put myArray size constant
• addi    $t4   ,   $t0   , 90   #Loop counter
• addi    $t9 ,   $t9 , 1     #input counter
• addi    $s5 ,   $s5 , 10   #Division

#Here, Now we want to prompt the user what they must do

• li    $v0,     4 #load immediate $v0,    4 , tells the compiler that we will pass a string value to $a0, which is a cout command in C++
• la       $a0,     prompt
• syscall # This system call will print the message as mentioned above prompt

# Now it will load the nxtline variable, which hold the value of \n to go to the next line, see below

• li         $v0,     4
• la       $a0,     nxtline
• syscall

input :

      #user enter 10 integers

• beq    $t1,   $t0, continue _{^{#it will compare the first register with the second register}}

# This below will count the number of integers entered, it will count the number of variables

• move $s0,     $t9
• li         $v0,      i
• syscall

#Now below code will differentiate between the input counter and the input that will be entered.

• li     $v0 , 4
• la    $ao , colon
• syscall

#Now to scan the values from the user, this command is same as the cin command in C++

• li   $v0   , 5
• syscall
• move   $t2   , $v0

• sw $t2, myArray($t1) #Store word, it will transfer the values inside first register into second register.
• addi   $t1,   $t1,   4 #This is basically to update the array position, here it will add 4 which means 4 bytes for the integer to go to the next position in the array
• addi    $t9,   $t9,   1 #Update for input counter
• j input #jump command , means program will go to the address that comes after the command , Here it will go back to input.

continue:

#Reinitialize register

move $t1, $zero For array(x)

move $t2, $zero

addi $t2, $t2, 4 #For array(x+1)

move $so, $zero

addi $so, $s0, 1 #conditon check

Sort :

#This code will sort the array, and checks conditions for swapping elements

• beg $t3, $t4, calculation    #finish loop
• beg   $t2, $t0, continue #Reinitialize array

• lw $t5, myArray($t1) #load word , description given above
• lw $t6, myArray($t2)   #load word , description given above

• addi $t3, $t3,   $t6 #update for the loop counter
• slt $t7, $t5, $t6 #checks the condition (set less than), it will compare the n register to n+ 1 register
• beg $t7,   $s0, swap # used to sort the element in the decending order and it will help to swap the elements to arrage the elements in order
• addi $t1, $t1, 4
• addi $t2, $t2, 4
• j sort

swap:

#swap array elements

• sw   $t5, myArray($t2)
• sw   $t6 , myArray($t1)

#command to update array position below

• addi $t1, $t1, 4
• addi $t2, $t2, 4
• j sort

calculation:

#After sorting reinitialize the register

• move $t1, $zero                 #Array elements
• move $t2, $zero             #Temporary holder
• move $t3, $zero              #First array element
• move $t4, $zero
• move $t5, $zero
• move $t6, $zero
• move $t7, $zero

Hope This above program will help you to better understandment of the sorting program