.data
str:
        .asciiz "Per"
        .asciiz "Per aspera, ad astra!"
msg:
        .asciiz "The length of string \n   \"%/a1/s\"\nis %/v1/d.\n"
        .word 123, 0x123


        .text
        .globl __start
__start:
        la $a0, str             # Load address of string.
        jal strlen              # Call strlen procedure.
        nop
        la $a1, str             # Load address of string to $a1
        addi $v1, $v0, 0        # Move length of string to $v1
        addi $v0, $0, 11        # System call code for message.
        la $a0, msg             # Address of message.
        syscall
        addi $v0, $0, 10        # System call code for exit.
        syscall

strlen:
        ## Register Usage
        #
        # $a0: Address of first character of string.
        # $v0: Return value, the length of the string.
        #

        addi $v1, $a0, 1   # Save starting address + 1, later used to find len.
        lb $t0, 0($a0)     # Load first character.
LOOP:
        beq $t0, $0, DONE  # Exit loop if at the end-of-string marker, a zero.
        addi $a0, $a0, 1   # Increment address to point at next character.
        j LOOP
        lb $t0, 0($a0)     # Load the next character.

DONE:

        jr $ra
        sub $v0, $a0, $v1