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; Version : 1.01
; Updated : 25/5/2020
; Copyright (C) : 2020 Gentoo-libre Install
; Licence : GPLv3+
; Description : Simple lowercase to capital program.
; Capitilises each lowercase ASCII char recieved in stdin and prints such to stdout. Exit only occurs if EOF is read.
; Done byte by byte for simplicity
section .text
global _start
_start: xor edi, edi ; file descriptor = stdin = 0
lea rsi, [rsp+8] ; buffer = address to store the bytes read
mov edx, 1 ; number of bytes to read
xor eax, eax ; SYSCALL number for reading from STDIN is 0
syscall ; make the syscall
test eax, eax ; If syscall returns 0 in rax, the character is EOF
je _exit ; if char is EOF: exit
cmp byte[rsp+8],'a' ;check if read char is below 'a'
jl newline ;if below 'a', it's not a lowercase char
cmp byte[rsp+8],'z' ;check if read char is equal to or below z
ja newline ;if not equal or above, it's not a lowercase char
sub byte[rsp+8], 32 ;subtract 32 from ASCII char to capitalise it
newline:mov edi, 1 ; file descriptor = stdout
lea rsi, [rsp+8] ; buffer = address to write to console
mov edx, 1 ; number of bytes to write
mov eax, 1 ; SYSCALL number for writing to STDOUT
syscall ; make the syscall
jmp _start ; read the next char
_exit: xor edi, edi ; set exit status = 0
mov eax, 60 ; SYSCALL number for EXIT
syscall ; make the syscall
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