##############################
#
# Binary to decimal converter
#
##############################

        .data
        .align 2
prompt:         .asciiz "\nInput> "
output:         .asciiz "\nDecimal = "
badinput:       .asciiz "\nBad input\n"
binin:          .space 64


        .text
        .globl  main


main:
        la      $a0,prompt              # Load first prompt
        li      $v0,4                   # Used in syscall for printing strings
        syscall

        li      $a1,64
        la      $a0,binin               # Store binary input number
        li      $v0,8                   # Used in syscall for storing strings
        syscall


atoi:
        la      $t0,binin               # Store address of binin in $t0
        li      $t3,0                   # Load 0 into $t3
        lb      $t1,0($t0)              # Load byte into $t1
        bne     $t1,'1',loop            # Do nothing if input is positive
        li      $t3,-1                  # Negative input; set everything to 1


loop:
        beq     $t1,'\n',final          # Check for end of string
        blt     $t1,'0',inputerr        # Make sure value is >= 0
        bgt     $t1,'1',inputerr        # Make sure value is <= 1

        addi    $t2,$t1,-48             # Store value of digit in $t2
        sll     $t3,$t3,1               # Shift one bit to multiply by 2
        add     $t3,$t3,$t2             # Add digit to current total
        addi    $t0,$t0,1               # Move pointer to next byte
        lb      $t1,0($t0)              # Load the next byte and loop

        b       loop


inputerr:                               # Display an error and jump
        la      $a0,badinput            #   back to beginning
        li      $v0,4
        syscall

        j       main


final:
        move    $a0,$t3
        li      $v0,1
        syscall

        j       main


Exit:
        li      $v0,10
        syscall