131 lines
1.9 KiB
NASM
131 lines
1.9 KiB
NASM
; THIS CODE HAS NOT BEEN TESTED AND IS NOT FULLY OPERATIONAL.
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; Problem Statement: Write x86 ALP to find the factorial of a given integer number on a command line by using recursion. Explicit stack manipulation is expected in the code.
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; Code from Microprocessor (SPPU - Second Year - Computer Engineering - Content) repository on KSKA Git: https://git.kska.io/sppu-se-comp-content/Microprocessor/
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; BEGINNING OF CODE
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%macro print 2
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mov rax,1
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mov rdi,1
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mov rsi,%1
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mov rdx,%2
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syscall
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%endmacro
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%macro exitprog 0
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mov rax,60
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xor rdi,rdi
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syscall
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%endmacro
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%macro gtch 1
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mov rax,0
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mov rdi,0
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mov rsi,%1
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mov rdx,1
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syscall
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%endmacro
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section .data
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nwline db 10
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m0 db 10,13,"----- Program to calculate factorial of a given number -----",10,10
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l0 equ $-m0
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m2 db 10,"Enter a number (2 digit HEX no.): "
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l2 equ $-m2
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m4 db 10,"The factorial is: "
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l4 equ $-m4
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factorial dq 1
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section .bss
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no1 resq 1
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input resb 1
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output resb 1
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section .text
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global _start
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_start:
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print m0,l0
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print m2,l2
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call getnum
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mov [no1],rax ;accept number
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gtch input ;to read and discard ENTER key ;pressed
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mov rcx,[no1]
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call facto
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mov rax,00
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print m4,l4
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mov rax,qword[factorial]
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call disphx16 ;displays a 8 digit hex number ;in rax
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exitprog
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facto:
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push rcx
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cmp rcx,01
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jne ahead
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jmp exit2
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ahead: dec rcx
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call facto
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exit2:
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pop rcx
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mov rax,rcx
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mul qword[factorial]
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mov qword[factorial],rax
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ret
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;Procedure to get a 2 digit hex no from user
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;number returned in rax
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getnum:
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mov cx,0204h
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mov rbx,0
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ll2:
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push rcx
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gtch input
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pop rcx
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mov rax,0
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mov al,byte[input]
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sub rax,30h
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cmp rax,09h
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jbe skip1
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sub rax,7
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skip1:
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shl rbx,cl
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add rbx,rax
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dec ch
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jnz ll2
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mov rax,rbx
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ret
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disphx16: ;displays a 16 digit hex number
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mov rbx,rax
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mov cx,1004h ;16 digits to display and 04 count ; to rotate
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ll6:
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rol rbx,cl
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mov rdx,rbx
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and rdx,0fh
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add rdx,30h
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cmp rdx,039h
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jbe skip4
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add rdx,7
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skip4:
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mov byte[output],dl
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push rcx
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print output,1
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pop rcx
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dec ch
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jnz ll6
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ret
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; END OF CODE
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