MIPS implementation of selection sort without manipulating the ra or sp register

Question

MIPS implementation of selection sort without manipulating the ra or sp registers. $a0 is the beginning of the array and $a1 is the size.

Explanation / Answer

.text j main # Jump to main-routine .data str1: .asciiz "Insert the array size " str2: .asciiz "Insert the array elements,one per line " str3: .asciiz "The sorted array is : " str5: .asciiz " " .text .globl main main: la $a0, str1 # Print of str1 li $v0, 4 # syscall # li $v0, 5 # Get the array size(n) and syscall # and put it in $v0 move $s2, $v0 # $s2=n sll $s0, $v0, 2 # $s0=n*4 sub $sp, $sp, $s0 # This instruction creates a stack # frame large enough to contain # the array la $a0, str2 # li $v0, 4 # Print of str2 syscall # move $s1, $zero # i=0 for_get: bge $s1, $s2, exit_get # if i>=n go to exit_for_get sll $t0, $s1, 2 # $t0=i*4 add $t1, $t0, $sp # $t1=$sp+i*4 li $v0, 5 # Get one element of the array syscall # sw $v0, 0($t1) # The element is stored # at the address $t1 la $a0, str5 li $v0, 4 syscall addi $s1, $s1, 1 # i=i+1 j for_get exit_get: move $a0, $sp # $a0=base address af the array move $a1, $s2 # $a1=size of the array jal isort # isort(a,n) # In this moment the array has been # sorted and is in the stack frame la $a0, str3 # Print of str3 li $v0, 4 syscall move $s1, $zero # i=0 for_print: bge $s1, $s2, exit_print # if i>=n go to exit_print sll $t0, $s1, 2 # $t0=i*4 add $t1, $sp, $t0 # $t1=address of a[i] lw $a0, 0($t1) # li $v0, 1 # print of the element a[i] syscall # la $a0, str5 li $v0, 4 syscall addi $s1, $s1, 1 # i=i+1 j for_print exit_print: add $sp, $sp, $s0 # elimination of the stack frame li $v0, 10 # EXIT syscall # # selection_sort isort: addi $sp, $sp, -20 # save values on stack sw $ra, 0($sp) sw $s0, 4($sp) sw $s1, 8($sp) sw $s2, 12($sp) sw $s3, 16($sp) move $s0, $a0 # base address of the array move $s1, $zero # i=0 subi $s2, $a1, 1 # lenght -1 isort_for: bge $s1, $s2, isort_exit # if i >= length-1 -> exit loop move $a0, $s0 # base address move $a1, $s1 # i move $a2, $s2 # length - 1 jal mini move $s3, $v0 # return value of mini move $a0, $s0 # array move $a1, $s1 # i move $a2, $s3 # mini jal swap addi $s1, $s1, 1 # i += 1 j isort_for # go back to the beginning of the loop isort_exit: lw $ra, 0($sp) # restore values from stack lw $s0, 4($sp) lw $s1, 8($sp) lw $s2, 12($sp) lw $s3, 16($sp) addi $sp, $sp, 20 # restore stack pointer jr $ra # return # index_minimum routine mini: move $t0, $a0 # base of the array move $t1, $a1 # mini = first = i move $t2, $a2 # last sll $t3, $t1, 2 # first * 4 add $t3, $t3, $t0 # index = base array + first * 4 lw $t4, 0($t3) # min = v[first] addi $t5, $t1, 1 # i = 0 mini_for: bgt $t5, $t2, mini_end # go to min_end sll $t6, $t5, 2 # i * 4 add $t6, $t6, $t0 # index = base array + i * 4 lw $t7, 0($t6) # v[index] bge $t7, $t4, mini_if_exit # skip the if when v[i] >= min move $t1, $t5 # mini = i move $t4, $t7 # min = v[i] mini_if_exit: addi $t5, $t5, 1 # i += 1 j mini_for mini_end: move $v0, $t1 # return mini jr $ra # swap routine swap: sll $t1, $a1, 2 # i * 4 add $t1, $a0, $t1 # v + i * 4 sll $t2, $a2, 2 # j * 4 add $t2, $a0, $t2 # v + j * 4 lw $t0, 0($t1) # v[i] lw $t3, 0($t2) # v[j] sw $t3, 0($t1) # v[i] = v[j] sw $t0, 0($t2) # v[j] = $t0 jr $ra

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