;; bto.asm Binary To Octal
;; version 0.0.3a
;;
;; Copyright 2016 Kevin G. Austin
;;
;; Licensed under the Apache License, Version 2.0 (the "License");
;; you may not use this file except in compliance with the License.
;; You may obtain a copy of the License at
;; 
;;     http://www.apache.org/licenses/LICENSE-2.0
;; 
;; Unless required by applicable law or agreed to in writing, software
;; distributed under the License is distributed on an "AS IS" BASIS,
;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
;; See the License for the specific language governing permissions and
;; limitations under the License.
;;
;; to build :
;; For 32 bit Linux systems
;; nasm -f elf bto.asm && ld -s bto.o -o bto
;; For 64 bit Linux systems
;; nasm -f elf64 bto.asm && ld -s bto.o -o bto
;;
;; Uncomment the next line for 32 bit systems
;; BITS 32
;; Uncomment the next line for 64 bit systems
;; BITS 64
  

section .bss
		ibufr:		resb	1	; reserve 1 byte input buffer
		obufr:		resb	1	; reserve 1 byte output buffer
		loopctr:	resb	1	; reserve 1 byte loop counter

section .text

		global _start

_start:		

;; Loop once for each char of output.

		mov	al, 16			; set the loop counter
charloop:
		mov	esi, loopctr
		mov	[byte esi], byte al	; save the loop counter

		mov	al, 3			; syscall 3 = read
		mov	bl, 0			; 0 = stdin
		mov	ecx, ibufr		; pointer to buffer
		mov	dl, 1			; read 1 char
		int	0x80			; syscall
		or	eax, eax		; test return
		jle	done			; <= 0 means done

		mov	esi, ibufr		; set esi to input pointer
		mov	al, [esi]		; move char to al
		shr	al, 6			; get the top two bits
		add	al, 0x30		; convert to printable

		call	writechar

		mov	esi, ibufr		; set esi to input pointer
		mov	al, [esi]		; move char to al
		shr	al, 3			; get middle bits
		and	al, 7
		add	al, 0x30		; convert to printable

		call	writechar

		mov	esi, ibufr		; set esi to input pointer
		mov	al, [esi]		; move char to al
		and	al, 7			; get last three bits
		add	al, 0x30		; convert to printable

		call	writechar

		mov	al, byte ' '

		call	writechar

		mov	esi, loopctr
		mov	al, [esi]		; move char to al
		dec	al			; decrement it

		jg	charloop		; loop if counter > 0

		mov	al, byte 10		; counter = 0 move \n to buffer

		call	writechar

		mov	al, 16			; set the counter back to 16

		jmp	charloop

done:
		mov	esi, obufr		; set esi to output pointer
		mov	[byte esi], byte 10	; move final \n to buffer
		mov	eax, 4			; syscall 4 = write
		mov	bl, 1			; 1 = stdout
		mov	ecx, obufr		; pointer to char buffer
		mov	dl, 1			; write 1 char
		int	0x80			; syscall

		xor	eax, eax			; clear eax
		inc	eax				; set syscall to exit (= 1)
		int	0x80				; syscall

writechar:
		mov	esi, obufr		; set esi to output pointer
		mov	[byte esi], byte al	; put result in output buffer
		mov	eax, 4			; syscall 4 = write
		mov	bl, 1			; 1 = stdout
		mov	ecx, obufr		; pointer to char buffer
		mov	dl, 1			; write 1 char
		int	0x80			; syscall
		or	eax, eax		; test return
		jle	done			; <= 0 means failure
		ret