; THIS CODE HAS BEEN TESTED AND IS FULLY OPERATIONAL.

; Problem Statement: Write X86/64 ALP to perform non-overlapped block transfer (WITH string specific instructions). Block containing data can be defined in the data segment.

; Code from Microprocessor (SPPU - Second Year - Computer Engineering - Content) repository on KSKA Git: https://git.kska.io/sppu-se-comp-content/Microprocessor/


; BEGINNING OF CODE
%macro print 2
mov rax,1			; Standard output
mov rdi,1			; Input write
mov rsi,%1		; Display message address
mov rdx,%2		; Message length
syscall				; Interrupt for kernel in 64-bit
%endmacro

section .data 
msg db 10, 'Block contents before transfer',10,13		; Initializing the display message
msglen equ $-msg																		; Length of the message

msg2 db 10, 'Block contents after transfer',10,13		; Initializing the display message
msg2len equ $-msg2																	; Length of the message

msg3 db 10,13, 'Source block' 
msg3len equ $-msg3 

msg4 db 10,13, 'Destination block'                                                                                     
msg4len equ $-msg4 

space db ' '						; Space between the variables to be displayed
spacelen equ $-space		; Initializing length of space

srcblk db  10h,20h,30h,40h,50h		; Contents of the src block
destblk db 0,0,0,0,0							; Initial contents of dest block
cnt equ 5													; Count is equal to 5 as 5 variables declared

section .bss			; Storing the array of data/reserving space for the data
ans resb 4				; Reserve buffer ans of 4-bytes(8-bits each)
;destblk resb 5		; Reserve buffer destblk of 5-bytes

section .text
global  _start				; Starting of the main program 
_start:
	print msg,msglen		; Displaying the msg1
	mov rsi,srcblk			; Move contents of source blk to rsi
	call disp_block			; Calling procedure disp_block
	cld									; Clear direction flag
	mov rcx,05h					; Move 05h into rcx register
	mov rsi,srcblk			; Move contents of src block into rsi
	mov rdi,destblk			; Move contents of dest blok into rdi
	rep movsb						; Repeat move string byte

	print msg2,msg2len	; Displaying the msg2
	mov rsi,destblk			; Move contents of destblk into rsi
	call disp_block			; Calling procedure disp_block
	mov rax,60					; Exit system call
	xor rdi,rdi					; Clearing rdi (by using xor) so that we get 0 in destblk
	syscall							; Interrupt for kernel in 64-bit

disp_block:			; Procedure disp_block
	mov rbp,cnt		; Base pointers

back:                                                            
	mov al,[rsi]		; Move contents of rsi to al
	push rsi				; Push contents of rsi
	call disp_8			; Calling the disp_8 procedure
	print space,1		; Intialize one byte for space
	pop rsi					; Pop contents of rsi
	inc rsi					; Increment rsi by 1
	dec rbp					; Decrement cnt through rbp
	jnz back				; Jump to loop back if not zero
	ret							; Return

disp_8:						; Procedure disp_8 
	mov rsi,ans+1		; Move the contents of ans buffer into rsi
	mov rcx,2				; Move 2 into the rcx register
                                  
back1:					; Loop back1
	mov rdx,0			; Clear rdx
	mov rbx,16		; Move 16 into rbx register
	div rbx				; Divide rax register by rbx register
	cmp dl,09h		; Compare the contents of dl register with 09h
	jbe add_30		; If compared value is below (less) than add 30h
	add dl ,07h		; Add 07h to dl register

add_30:					; add_30 label 
	add dl,30h		; Add 30h to the contents of dl register 
	mov[rsi],dl		; Move contents of dl into rsi 
	dec rsi				; Decrement rsi 
	dec rcx				; Decrement rcx    
	jnz back1			; Jump if not zero to loop back1     
	print ans,2		; Print the result      
ret							; Return
; END OF CODE