Assignment 4 encryption utility

.data
.eqv			PASS_BUFFER_SZ 257
.eqv			STR_BUFFER_SZ	256
.eqv			XOR_BUFFER_SZ 	1024
.eqv			XOR_BUFFER1_SZ	1024
.eqv			FILE_BUFFER_SZ	257
.eqv	CONSOLE_RECEIVER_CONTROL           0xffff0000
.eqv	CONSOLE_RECEIVER_READY_MASK        0x00000001
.eqv	CONSOLE_RECEIVER_DATA              0xffff0004
.eqv	ISO_LF			0x2A  # Line feed (newline)
.eqv	SYS_PRINT_CHAR	0xB
.eqv	EXIT_Enter			0x0A


FILE_BUFFER:		.space FILE_BUFFER_SZ
STR_BUFFER:		.space	STR_BUFFER_SZ
PASS_BUFFER:		.space 	PASS_BUFFER_SZ
XOR_BUFFER:		.space  XOR_BUFFER_SZ
XOR_BUFFER1:		.space	XOR_BUFFER1_SZ
sourcefilepath:		.asciiz  "Enter the path for the source file: "
destinationfilepath:	.asciiz  "Enter the path for the destinationfile: "
passphrase:		.asciiz	 "Enter the passphrase: "
asterisk:		.asciiz "*"
newline:		.asciiz "\n"
.align 2
.text
.globl main
main:
		jal sourcefile
		jal passphrase_sub
		jal destinationfile
		
		#end program
		li $v0, 10
		syscall

#ask user to read the file 
#load the content from the sourcefile
sourcefile:
		#print the statement ask user to input the path of the sourcefile
		la $a0, sourcefilepath
		li $v0, 4
		syscall
	
		#User input saved into str_buffer
		la $a0, STR_BUFFER
		li $a1, STR_BUFFER_SZ
		li $v0, 8
		syscall
	
		li $v0, 13		#open the file
		la $a0, STR_BUFFER
		li $a1, 0
		li $a2, 1
		syscall
		move $s0, $v0	
		jr $ra
#collect passphrase from user input 
#print them with * into the console		
passphrase_sub:
		#print out the statement ask user input the passpharse
		li $v0, 4		
		la $a0, passphrase	#prompts user input for the passpharse
		syscall
		
		#save the userinput into the buffer
		li	$t1, EXIT_Enter
		la 	$s0, PASS_BUFFER
	    # Spin-wait for key to be pressed
    key_wait:

	    lw      $t0, CONSOLE_RECEIVER_CONTROL
	    andi    $t0, $t0, CONSOLE_RECEIVER_READY_MASK  # Isolate ready bit
	    beqz    $t0, key_wait
    
	    # Read in new character from keyboard to low byte of $a0
	    # and clear other 3 bytes of $a0
	   	lbu     $a0, CONSOLE_RECEIVER_DATA
		beq	$a0, $t1, destinationfile
		sb	$a0, 0($s0)
		addi $s0, $s0, 1

	    # Print character and newline
	    	li      $v0, SYS_PRINT_CHAR
	    	li      $a0, ISO_LF
	    	syscall
		b key_wait

#ask user to input the path for the destination file
#doing the xor function then write the result into the destinationfile		
destinationfile:
		#print a new line
		li $v0, 4
		la $a0, newline
		syscall
		
		#print the statement ask user to input the destination file path
		li $v0, 4
		la $a0, destinationfilepath
		syscall
		
		#load the buffer into file buffer
		la $a0, FILE_BUFFER
		li $a1, FILE_BUFFER_SZ
		li $v0, 8
		syscall
		
		#open the file, if the file doesn't exist then create a new one
		la $a0, FILE_BUFFER
		li $a1, 1
		li $a2, 0
		li $v0, 13
		syscall
		move $s1, $v0
		
		la $s6 PASS_BUFFER
		
	
#doing the xor instruction
#save the result into the destination file	
XOR_perform:
		li $t2, 0
		li $t1, 0
		li $v0, 14		#read mode
		move $a0, $s0
		la $a1, XOR_BUFFER
		li $a2, XOR_BUFFER_SZ
		syscall
		move $t0, $v0
		#xor instrusction using passphrase buffer and xor buffer
		la $s7, XOR_BUFFER
		lb $t3, 0($s6)
		lb $t2, 0($s7)
		addi $s6, $s6, 1
		addi $s7, $s7, 1
		xor $t3, $t2, $t3
		#save the xor character into new buffer
		la $s5, XOR_BUFFER1
		sb $t3, 0($s5)
		addi $s5, $s5, 1
		beq $0 $v0, close_src
		j XOR_perform
		
		
close_src:	
		#write new file
		move $a0, $s1
		la $a1, XOR_BUFFER1
		move $a2, $v0
		li $v0, 15
		syscall
		#close the source file
		li $v0, 16
		move $a0, $s0
		syscall
		#close the destination file				
		li $v0, 16
		move $a0, $s1
		syscall
		
		jr $ra