.data
BufferSize: .word 32
Newline: .asciiz "\r\n"
Separator_Text: .asciiz " => "
Prompt_Text: .asciiz "Enter a string: "

.text
main:
    jal prompt
    jal print_separator
    jal loop_start
    jal print_string
    j exit

prompt:
    # Print prompt string
    li $v0, 4
    la $a0, Prompt_Text
    syscall
    # Alloc string buffer
    li $v0, 9
    lw $a0, BufferSize
    syscall
    # Read string input, $s0 contains beginning of string addr
    move $s0, $v0
    move $a0, $s0
    li $v0, 8
    lw $a1, BufferSize
    syscall
    # Reset index
    li $s1, 0
    # Return
    jr $ra

# Preserve return address and begin loop
loop_start:
    move $s2, $ra
    j loop

# Loop through characters in buffer
loop:
    lw $t0, BufferSize
    bge $s1, $t0, loop_done
    jal tolower
    addi $s1, $s1, 1
    j loop

# Return to preserved address
loop_done:
    jr $s2

# $s0 - Base String Address
# $s1 - Byte Index
tolower:
    # Load byte
    add $t0, $s0, $s1
    lb $t1, ($t0)
    # Check if uppercase character
    li $t2, 65
    blt $t1, $t2, tolower_skip
    li $t2, 90
    bgt $t1, $t2, tolower_skip
    # Perform lowercase change
    addi $t1, $t1, 32
    # Store byte
    sb $t1, ($t0)
    # Return
    jr $ra

tolower_skip:
    jr $ra

# Print separator string
print_separator:
    li $v0, 4
    la $a0, Separator_Text
    syscall
    jr $ra

# Print string @ addr in $s0
print_string:
    li $v0, 4
    la $a0, ($s0)
    syscall
    jr $ra

exit:
    li $v0, 10
    syscall