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  1. ; Simon Whitehead
  2.  
  3. section .data
  4.  
  5.     newline db 10
  6.  
  7.     number dd 123456789	; The number to print
  8.  
  9.     ; Syscall information
  10.     sys_exit equ 1
  11.     sys_write equ 4
  12.  
  13.     ; Streams
  14.     stdout equ 1
  15.  
  16.     ; Constants
  17.     BUFFER_SIZE equ 10
  18.  
  19. section .bss
  20.  
  21.     numbuf resb BUFFER_SIZE		; A buffer to store our string of numbers in
  22.  
  23. section .text
  24.  
  25. global _start
  26.  
  27. _start:
  28.  
  29.     mov rdi,[number]	; Move the number (123456789) into rax
  30.     call itoa			; call the function
  31.  
  32.     ; Write the string returned in rax out to stdout
  33.     mov rdi,rax		; The string pointer is returned in rax - move it to rdi for the function call
  34.     mov rsi,rcx
  35.     call print
  36.  
  37.     ; Write the newline character to stdout
  38.     mov rdi,newline
  39.     mov rsi,1
  40.     call print
  41.  
  42.    ; Exit
  43.     mov rax,sys_exit
  44.     mov rbx,0
  45.  
  46.     int 0x80
  47.  
  48. ; Args: (rdi: char*, rsi: int)
  49. print:
  50.  
  51.     mov rax,sys_write
  52.     mov rbx,stdout
  53.     mov rcx,rdi
  54.     mov rdx,rsi
  55.  
  56.     int 0x80
  57.  
  58.     ret
  59.  
  60. itoa:
  61.  
  62.     push rbp		
  63.     mov rbp,rsp
  64.     sub rsp,4		; allocate 4 bytes for our local string length counter
  65.  
  66.     mov rax,rdi		; Move the passed in argument to rax
  67.     lea rdi,[numbuf+10]	; load the end address of the buffer (past the very end)
  68.     mov rcx,10		; divisor
  69.     mov [rbp-4],dword 0	; rbp-4 will contain 4 bytes representing the length of the string - start at zero
  70.  
  71. .divloop:
  72.     xor rdx,rdx		; Zero out rdx (where our remainder goes after idiv)
  73.     idiv rcx		; divide rax (the number) by 10 (the remainder is placed in rdx)
  74.     add rdx,0x30	; add 0x30 to the remainder so we get the correct ASCII value
  75.     dec rdi		; move the pointer backwards in the buffer
  76.     mov byte [rdi],dl	; move the character into the buffer
  77.     inc dword [rbp-4]	; increase the length
  78.  
  79.     cmp rax,0		; was the quotient zero?
  80.     jnz .divloop	; no it wasn't, keep looping
  81.  
  82.     mov rax,rdi		; rdi now points to the beginning of the string - move it into rax
  83.     mov rcx,[rbp-4]	; rbp-4 contains the length - move it into rcx
  84.  
  85.     leave		; clean up our stack
  86.     ret
  87.  
Success #stdin #stdout 0s 156KB
comments (?)
stdin
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Standard input is empty
stdout
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123456789
https://ideone.com/yG9kSK
language:
Assembler 64bit (nasm 2.14)
created:
6 years ago
visibility:
public

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