#Barcode 39 decoding
#--------------------------------
.eqv BMP_FILE_SIZE 90122
.eqv BYTES_PER_ROW 1800

.data
.align 4
res:        .space 2
image:  .space BMP_FILE_SIZE
#PROMPTS:
prompt:         .asciiz "After:\n "
prompt1:            .asciiz "Please enter which line should be checked:\n "
prompt2:            .asciiz "Prompt checked: \n "
promptb:            .asciiz "black \n "
promptw:            .asciiz "white \n "
enter:          .asciiz "\n"
promptf:            .asciiz "fat \n "
promptt:            .asciiz "thin \n "
#ERRORS:
dsc_error_message:  .asciiz     "File descriptor error!"
h_error_message:    .asciiz "Header error!"
size_error_message: .asciiz "Size error!"
f_error_message:    .asciiz "Format error!"


buffer:         .space  2
header:         .space  54
width:          .word   600
height:         .word   50

fname:          .asciiz     "/home/orzelke/Assmeblert/3.bmp"
.text
main:
    jal read_bmp
    #input y coordinate:
    li  $v0,    4
    la  $a0, prompt1
    syscall

    #input y coordinate:
    li  $v0,    5
    syscall
    move    $t7,    $v0
    li  $t8,    50
    sub     $t7,    $t8,    $t7

    li  $a0, 0  #x
    la  $a1, ($t7)      #y
    xor $t7,    $t7, $t7
    j   loop_condition








get_pixel:
#description:
#   returns color of specified pixel
#arguments:
#   $a0 - x coordinate
#   $a1 - y coordinate - (0,0) - bottom left corner

    la  $a0, ($t7)


    la $t1, image + 10  #adress of file offset to pixel array
    lw $t2, ($t1)       #file offset to pixel array in $t2
    la $t1, image       #adress of bitmap
    add $t2, $t1, $t2   #adress of pixel array in $t2

    li  $t0,    0

    #pixel address calculation
    mul $t1, $a1, BYTES_PER_ROW #t1= y*BYTES_PER_ROW
    move $t3, $a0
    sll $a0, $a0, 1
    add $t3, $t3, $a0   #$t3= 3*x
    add $t1, $t1, $t3   #$t1 = 3x + y*BYTES_PER_ROW
    add $t2, $t2, $t1   #pixel address
#t2 holds pixel adress
    #get color
    lb  $v0,    ($t2)
    move $t4,   $v0
    #if white -> loop_condition
    bnez    $t4,    loop_condition
    bgtz    $t9,    loop_condition


find_width_thin: #t9 holds width

    addiu   $t9,    $t9, 1
    addiu   $t2,    $t2,    3
    lb  $v0,    ($t2)
    beqz    $v0,    find_width_thin
    li  $t8,    3
    mul $t6,    $t9,    $t8 #how many bytes we need to go back
    sub $t2, $t2,   $t6
    xor $t8,    $t8,    $t8
    li  $v0,    4
    la  $a0, prompt
    subiu   $t2,    $t2, 3
    j   decoding_prep

loop_condition:
    addiu $t7, $t7, 1
    lw  $t5,    width
    beq $t7,    $t5, exit
    j   get_pixel

decoding_prep:
    li  $t8,    9   #after 9 bars/spaces we got new symbol
decoding:

    addiu $t2,  $t2, 3
    lb  $t4,    ($t2)

    beqz    $t4,    black

white:
    addiu   $s1, $s1, 1
    bgtz    $s2,    saveb

    j loop_condition2
black:
    addiu   $s2, $s2, 1
    bgtz    $s1,    savew

    j loop_condition2
savew:
    la  $s4,    ($s1)
    li  $s1, 0
    bgt $s4, $t9,    fat

    j thin
saveb:
    la  $s4,    ($s2)
    li  $s2, 0
    bgt $s4,    $t9 fat
    j thin
fat:
    li  $s3,    10
    mul $s5,    $s5, $s3
    addiu   $s5,    $s5, 2
    addiu   $t0,    $t0,    1
    j   loop_condition2
thin:
    li  $s3,    10
    mul $s5,    $s5, $s3
    addiu   $s5,    $s5,    1
    addiu   $t0,    $t0,    1

loop_condition2:
    beq $t0,    $t8,    print
    addiu $t7, $t7, 1
    lw  $t5,    width
    beq $t7,    $t5, exit
    j   decoding

print:
    li  $v0,    1
    la  $a0,    ($s5)
    syscall
    li  $v0,    4
    la  $a0,    enter
    syscall
    li  $t0,    0
    li  $s5,    0
skip_to_black:
    li  $v0,    4
    la  $a0,    enter
    syscall
    addiu   $t2,    $t2,    3
    lb  $t4,    ($t2)
    beqz    $t4,    black
    li  $s5,    0
    j   skip_to_black

read_bmp:
#description:
#   reads the contents of a bmp file into memory
#arguments:
#   none
#return value: none
    sub $sp, $sp, 4     #push $ra to the stack
    sw $ra,4($sp)
    sub $sp, $sp, 4     #push $s1
    sw $s1, 4($sp)
#open file
    li $v0, 13
        la $a0, fname       #file name
        li $a1, 0       #flags: 0-read file
        li $a2, 0       #mode: ignored
        syscall
    move $s1, $v0      # save the file descriptor

    bltz    $s1,    dsc_error

#read file
    li $v0, 14
    move $a0, $s1
    la $a1, image
    li $a2, BMP_FILE_SIZE
    syscall

#close file
    li $v0, 16
    move $a0, $s1
        syscall

    lw $s1, 4($sp)      #restore (pop) $s1
    add $sp, $sp, 4
    lw $ra, 4($sp)      #restore (pop) $ra
    add $sp, $sp, 4
    jr $ra
dsc_error:
    li  $v0, 4
    la  $a0, dsc_error_message
    syscall
    j   exit

bitmap_error:
    li  $v0, 4
    la  $a0, h_error_message
    syscall
    j   exit

size_error:
    li  $v0, 4
    la  $a0, size_error_message
    syscall
    j   exit

format_error:
    li  $v0, 4
    la  $a0, f_error_message
    syscall
    j   exit

exit:
    li      $v0,    10
syscall