Question

Selection sort is often the first sorting algorithm covered in introductory computer science courses. Java code that uses selection sort to place the elements of an integer array into non-decreasing order is shown here:

public void swapNumbers(int i, int j)

{

​int temp = numbers[i];​ /* put numbers[i] somewhere to

keep it safe */

​numbers[i] = numbers[j]; /* put numbers[j] at index i */

​numbers[j] = temp;​ /* put numbers[i] at index j */

}

public void selectionSort(int[] numbers)

{

/* For every index in the array,

with the exception of the last one, */

for (int searcherIndex = 0; searcherIndex < numbers.length-1;

searcherIndex++)

{

​/* Assume that the number is where it's supposed to be */

​int correctIndex = searcherIndex;

​

​/*Try out other candidate indexes*/

​for (int candidateIndex = searcherIndex+1;

candidateIndex < numbers.length; candidateIndex++)

​{

​​/* If you find a smaller number,

make it's index the correct index */

​​if(numbers[candidateIndex] < numbers[correctIndex])

​​correctIndex = candidateIndex;

​}

​/* At this point correctIndex really will be

the correct index */

​swapNumbers (searcherIndex, correctIndex);

}

}

A similar C++ version (from Dr. Mock’s notes) and an example driver program is shown here:

void swap(int &a, int &b)

{

int temp = a;

a = b;

b = temp;

}

void selectionSort(int a[], int n)

{

for (int i = 0; i < n-1; i++)

{

int indexOfMin = i;

for (int j = i+1; j < n; j++)

{

if (a[j] < a[indexOfMin])

indexOfMin = j;

}

swap(a[i], a[indexOfMin]);

}

}

int main()

{

int a[] = {4, 5, 1, 354, 21, 45, 3};

for (int i = 0; i < 7; i++)

cout << a[i] << endl;

selectionSort(a, 7);

for (int i = 0; i < 7; i++)

cout << a[i] << endl;

}

For this assignment, you are required to translate one of these two high-level-language algorithms into a MIPS assembly language program that uses subroutines selectionSort and swap to sort an array of integers. Use the selected algorithm as in-line documentation for your MIPS source code. Be sure that both subroutines follow standard register use conventions, and utilize the stack frame technique shown in class for all subroutine calls. Your main method should use system calls to interactively display the contents of the array both before and after the call to selectionSort.

Answer 1

.file    1 ""
    .section .mdebug.abi32
    .previous
    .nan    legacy
    .module    fp=32
    .module    nooddspreg
    .abicalls
    .text
    .align    2
    .globl    swap
    .set    nomips16
    .set    nomicromips
    .ent    swap
    .type    swap, @function
swap:
    .frame    $sp,0,$31        # vars= 0, regs= 0/0, args= 0, gp= 0
    .mask    0x00000000,0
    .fmask    0x00000000,0
    .set    noreorder
    .set    nomacro
    j    $31
    nop

    .set    macro
    .set    reorder
    .end    swap
    .size    swap, .-swap
    .align    2
    .globl    selectionSort
    .set    nomips16
    .set    nomicromips
    .ent    selectionSort
    .type    selectionSort, @function
selectionSort:
    .frame    $sp,0,$31        # vars= 0, regs= 0/0, args= 0, gp= 0
    .mask    0x00000000,0
    .fmask    0x00000000,0
    .set    noreorder
    .set    nomacro
    j    $31
    nop

    .set    macro
    .set    reorder
    .end    selectionSort
    .size    selectionSort, .-selectionSort
    .section    .rodata.str1.4,"aMS",@progbits,1
    .align    2
$LC1:
    .ascii    "%d\000"
    .rdata
    .align    2
$LC0:
    .word    4
    .word    5
    .word    1
    .word    354
    .word    21
    .word    45
    .word    3
    .section    .text.startup,"ax",@progbits
    .align    2
    .globl    main
    .set    nomips16
    .set    nomicromips
    .ent    main
    .type    main, @function
main:
    .frame    $sp,80,$31        # vars= 32, regs= 5/0, args= 16, gp= 8
    .mask    0x800f0000,-4
    .fmask    0x00000000,0
    .set    noreorder
    .cpload    $25
    .set    nomacro
    addiu    $sp,$sp,-80
    lw    $5,%got($LC0)($28)
    lw    $25,%call16(memcpy)($28)
    sw    $18,68($sp)
    addiu    $18,$sp,24
    movz    $31,$31,$0
    .cprestore    16
    sw    $19,72($sp)
    sw    $17,64($sp)
    sw    $16,60($sp)
    sw    $31,76($sp)
    li    $6,28            # 0x1c
    addiu    $5,$5,%lo($LC0)
    .reloc    1f,R_MIPS_JALR,memcpy
1:    jalr    $25
    move    $4,$18

    lw    $28,16($sp)
    move    $17,$0
    lw    $16,%got($LC1)($28)
    li    $19,28            # 0x1c
    addiu    $16,$16,%lo($LC1)
    addu    $2,$18,$17
$L10:
    lw    $25,%call16(__printf_chk)($28)
    lw    $6,0($2)
    move    $5,$16
    li    $4,1            # 0x1
    .reloc    1f,R_MIPS_JALR,__printf_chk
1:    jalr    $25
    addiu    $17,$17,4

    lw    $28,16($sp)
    bne    $17,$19,$L10
    addu    $2,$18,$17

    move    $17,$0
    li    $19,28            # 0x1c
    addu    $2,$18,$17
$L11:
    lw    $25,%call16(__printf_chk)($28)
    lw    $6,0($2)
    move    $5,$16
    li    $4,1            # 0x1
    .reloc    1f,R_MIPS_JALR,__printf_chk
1:    jalr    $25
    addiu    $17,$17,4

    lw    $28,16($sp)
    bne    $17,$19,$L11
    addu    $2,$18,$17

    lw    $31,76($sp)
    lw    $19,72($sp)
    lw    $18,68($sp)
    lw    $17,64($sp)
    lw    $16,60($sp)
    move    $2,$0
    j    $31
    addiu    $sp,$sp,80