;WTFStopW : a simple stopwatch
;Copyright (C) 2018 Weber Yann
;
;This program is free software; you can redistribute it and/or modify
;it under the terms of the GNU General Public License as published by
;the Free Software Foundation; either version 3 of the License, or
;any later version.
;
;This program is distributed in the hope that it will be useful,
;but WITHOUT ANY WARRANTY; without even the implied warranty of
;MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;GNU General Public License for more details.
;
;You should have received a copy of the GNU General Public License
;along with this program.  If not, see <http://www.gnu.org/licenses/>.

; A simple precise stopwatch
; Build with : 
; nasm -felf64 wtfstopw.asm && ld wtfstopw.o -o wtfstopw

[bits 64]

section .data

	STRUC TIMESPEC_STRUC
		.tv_sec: resq 1
		.tv_nsec: resq 1
	ENDSTRUC


	%macro TIMESPEC 1
		%1: ISTRUC TIMESPEC_STRUC
			at TIMESPEC_STRUC.tv_sec, dq 0
			at TIMESPEC_STRUC.tv_nsec, dq 0
		IEND
		%define %1.tv_sec %1+TIMESPEC_STRUC.tv_sec
		%define %1.tv_nsec %1+TIMESPEC_STRUC.tv_nsec
	%endmacro

	TIMESPEC ts_start
	TIMESPEC ts_cur

	ts_sleep:
		tv_sleep_s dd 0,0
		tv_sleep_us dd 10000000,0 


	;; 1/2s sleep
	;ts_sleep:
	;	tv_sleep_s dq 0
	;	tv_sleep_us dq 500000000


	faultmsg: db "fault", 0xA
	faultmsglen: equ $ - faultmsg

	msg:	db "0 Hello, world!", 10
	msglen: equ $ - msg

	hours: db "000000000"
	timestr: db ":00:00.0000    ", 0x0D
	timestrlen: equ $ - timestr

	nl: db 0x0A
	buf: db 0



section .text
global _start

_start:

; set stdin non blocking
xor rdx, rdx
xor rdi, rdi
mov rax, 72 ; fcntl
mov rsi, 3 ; F_GETFL
syscall
mov rdx, rax
or rdx, 0x800 ; O_NONBLOCK
dbg:
mov rax, 72 ; fcntl
mov rsi, 4 ; F_SETFL
syscall
cmp rax, 0
jne fault

mov rax, 228 ; clock_gettime
mov rdi, 0 ; CLOCK_REALTIME
mov rsi, ts_start
syscall


print_time:
	; updating ts_cur time
	mov rax, 228 ; clock_gettime
	mov rdi, 0 ; CLOCK_REALTIME
	mov rsi, ts_cur
	syscall

	mov rax, [ts_cur.tv_nsec]
	mov rbx, [ts_start.tv_nsec]
	sub rax, rbx
	cmp rax, 0
	jge print_time_us_cont
	; negativ result
	add rax, 1000000000
	mov rbx, [ts_cur.tv_sec]
	sub rbx, 1
	mov [ts_cur.tv_sec], rbx
	print_time_us_cont:
	xor rdx, rdx
	mov rcx, 100000
	div rcx
	; set the us char in timestr
	mov r8, timestr
	add r8, 10 ; r8 points on last char before \r
	mov r9, 4 ; r9 count the number of digits
	print_time_us_loop:
		xor rdx, rdx
		mov rcx, 10
		div rcx
		add dl, 0x30
		mov [r8], dl
		sub r8, 1
		sub r9, 1
		cmp r9, 0
		jg print_time_us_loop

	; handling seconds, minutes & hours
	mov rax, [ts_cur.tv_sec]
	mov rbx, [ts_start.tv_sec]
	sub rax, rbx
	; rax now contain elapsed seconds
	; filling timestr with seconds & minutes

	xor rdx, rdx
	mov rcx, 10
	div rcx
	add dl, 0x30
	mov byte [timestr + 5], dl

	xor rdx, rdx
	mov rcx, 6
	div rcx
	push rax
	add dl, 0x30
	mov byte [timestr + 4], dl

	xor rdx, rdx
	mov rcx, 10
	div rcx
	add dl, 0x30
	mov byte [timestr + 2], dl

	pop rax
	xor rdx, rdx
	mov rcx, 6
	div rcx
	add dl, 0x30
	mov byte[timestr + 1], dl

	; filling the hours buffer
	; r8 will contain our digits counter : max is 8
	mov r8, 8
	print_time_hours_loop:
		mov rcx, 10
		xor rdx, rdx
		div rcx
		add dl, 0x30
		cmp rax, 0
		jne print_time_hours_print_mod
		cmp rdx, 0
		je print_time_hours_loop_end

		print_time_hours_print_mod:
		mov r9, hours
		add r9, r8
		mov byte [r9], dl
		cmp r8, 0
		je fault
		sub r8, 1
		cmp rax, 0
		jne print_time_hours_loop
	print_time_hours_loop_end:

	; print hours + timestr
	add r8, 1
	cmp r8, 7
	jle print_time_hours_cont
	mov r8, 7 ; maximum value for r8
	print_time_hours_cont:
	mov r9, hours
	add r9, r8
	mov rcx, 9
	sub rcx, r8 ; rcx is hours size 
	add rcx, timestrlen ; add to timestrlen

	mov rax, 1 ; write
	mov rdi, 1 ; stdout
	mov rsi, r9 ; start hours pointer
	mov rdx, rcx ; size to timestr end
	syscall

	; Attempt to read from stdin
	; if something read, enter has been pressed
	mov rax, 0
	mov rdi, 0
	mov rsi, buf
	mov rdx, 1
	syscall
	cmp rax, 0
	jge flush_stdin ; flush stdin and exit

	mov rax, 35 ; nanosleep
	mov rdi, ts_sleep
	mov rsi, 0
	syscall

	jmp print_time ; main loop

flush_stdin:
	mov rax, 0
	mov rdi, 0
	mov rsi, buf
	mov rdx, 1
	syscall
	cmp rax, 0
	je newline_exit
	jg flush_stdin

exit:
	mov rax, 60 ; sys_exit
	mov rdi, 0 ; OK
	syscall
fault:
	mov rax, 1 ; write
	mov rdi, 2 ; stderr
	mov rsi, nl
	mov rdx, 1
	syscall
	mov rax, 1
	mov rsi, faultmsg
	mov rdx, faultmsglen
	syscall

	mov rax, 60 ; sys_exit
	mov rdi, 1 ; failure
	syscall

newline_exit:
	mov rax, 1
	mov rdi, 1
	mov rsi, nl
	mov rdx, 1
	syscall
	jmp exit

.end: