9.3: Printing an Array

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This first program presented here shows how to access arrays by creating a PrintIntArray subprogram that prints the elements in an integer array. Two variables are passed into the subprogram, $a0 which is the base address of the array, and $a1, which is the number of elements to print. The subprogram processes the array in a counter loop, and prints out each element followed by a ",". The pseudo code for this subprogram follows.

Subprogram PrintIntArray(array, size)
{
    print("[")
    for (int i = 0; i < size; i++)
    {
        print("," + array[i])
    }
    print("]")
}

The following is the subprogram in assembly, along with a test main program to show how to use it.

Program 9-3: Printing an array of integers

.text
.globl main
main:
    la $a0, array_base
    lw $a1, array_size
    jal PrintIntArray
    jal Exit
.data
    array_size: .word 5
    array_base:
        .word 12
        .word 7
        .word 3
        .word 5
        .word 11

.text
# Subprogram: PrintIntArray
# Purpose: print an array of ints
# inputs: $a0 - the base address of the array
#         $a1 - the size of the array
#
PrintIntArray:
    addi $sp, $sp, -16    # Stack record
    sw $ra, 0($sp)
    sw $s0, 4($sp)
    sw $s1, 8($sp)
    sw $s2, 12($sp)
    
    move $s0, $a0         # save the base of the array to $s0
    
    # initialization for counter loop
    # $s1 is the ending index of the loop
    # $s2 is the loop counter
    move $s1, $a1
    move $s2, $zero
    
    la $a0 open_bracket    # print open bracket
    jal PrintString

loop:
    # check ending condition
    sge $t0, $s2, $s1
    bnez $t0, end_loop
    
        sll $t0, $s2, 2    # Multiply the loop counter by 4 to get offset (each element is 4 big).
        add $t0, $t0, $s0  # address of next array element
        lw $a1, 0($t0)     # Next array element
        la $a0, comma
        jal PrintInt       # print the integer from array
        
        addi $s2, $s2, 1   #increment $s0
        b loop
end_loop:

    li $v0, 4              # print close bracket
    la $a0, close_bracket
    syscall
    
    lw $ra, 0($sp)
    lw $s0, 4($sp)
    lw $s1, 8($sp)
    lw $s2, 12($sp)        # restore stack and return
    addi $sp, $sp, 16
    jr $ra

.data
    open_bracket:    .asciiz "["
    close_bracket:   .asciiz "]"
    comma:           .asciiz ","
.include "utils.asm"

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