Answer to Question #330239 in Assembler for Faisal

Question

Write a procedure that reads a text-paragraph from a file and then prints the number of characters on the screen.

Answer 1

# MIPS assembler
# Mars simulator
#------------------------------
    .data
fnf:    .ascii  "The file was not found: "
newL:    .asciiz  " "

# file_name_holder: the string that represents the file name
file_name_holder:     .asciiz  "1.txt"

descriptorScr: .word 0

# dat_buff : the buffer that you use to hold data (MAXIMUM: 300 bytes)
dat_buff: .space 300
        
    .text
main:

 # Open File (read-only)
    li    $v0, 13                    # Set $v0 to 13 for system call to open file
      la    $a0, file_name_holder    # Load file to read, $a0 set to address of string
                                # containing file name
    li    $a1, 0                    # Set read-only flag
    li    $a2, 0                    # Set mode
    syscall                        # the file descriptor will be returned in $v0
    
      blt    $v0, 0, err            # if failed to open file
    la $s0,    descriptorScr    
    sw $v0, 0($s0)            # Save file descriptor in $v0 to descriptorScr
 
     jal read_file        # function READ file
    add $a0,$zero,$v0    # $a0 contain number of characters (bytes) read    

    li $v0,1    # print number of characters (bytes) read    
    syscall        

     # Close Files
close:
    la $s0,    descriptorScr    #  file descriptor in  descriptorScr
    lw $a0, 0($s0)        # Load File Descriptor
    li    $v0, 16            # Set $v0 to 16 for system call to close file
    syscall    
    j done
    
    # Error
err:
    li    $v0, 4        # System call to print string
    la    $a0, fnf    # Load Error String
    syscall
 
# Done
done:
    li    $v0, 10        # Exit Syscall
    syscall
#------------------------------------------------
# function read file
# These function read text from the file to buffer
# output $v0 number bytes

read_file:    
    li    $v0, 14                # Set $v0 to 14 for system call to read file
    la $t0,    descriptorScr    #  file descriptor in  descriptorScr
    lw $a0, 0($t0)            # Load File Descriptor
    la    $a1, dat_buff        # Set $a1 to address of input dat_buff
    li    $a2, 300            # Set $a2 to number of characters to read
    syscall                    # $v0 will contain number of characters (bytes) read
                            # $v0 number bytes
    jr      $ra                # jump to parent call