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; -------------------------------------------------------------
; This is an OSX console program that writes a little triangle
; of asterisks to standard
; output. Runs on macOS only.
; nasm -fmacho64 triangle.asm && gcc hola.o && ./a.out
; -------------------------------------------------------------
global start
section .text
start:
mov rdx, output ; rdx holds address of next byte
to write
mov r8, 1 ; initial line length
mov r9, 0 ; number of stars written on line
so far
line:
mov byte [rdx], '*' ; write single star
inc rdx ; advance pointer
to next cell to write
inc r9 ; "count" number so
far on line
cmp r9, r8 ; did we reach the
number of stars for this line?
jne line ; not yet, keep
writing on this line
lineDone:
mov byte [rdx], 10 ; write a new line
char
inc rdx ; and move pointer
to where next char goes
inc r8 ; next line will be
one char longer
mov r9, 0 ; reset count of
stars written on this line
cmp r8, maxlines ; wait, did we
already finish the last line?
jng line ; if not, begin
writing this line
done:
mov rax, 0x02000004 ; system call for
write
mov rdi, 1 ; file handle 1 is
stdout
mov rsi, output ; address of string
to output
mov rdx, dataSize ; number of bytes
syscall ; invoke operating
system to do the write
mov rax, 0x02000001 ; system call for
exit
xor rdi, rdi ; exit code 0
syscall ; invoke operating
system to exit
section .bss
maxlines equ 8
dataSize equ 44
output: resb dataSize