; add 24 + 16 = 40 to the stack pointer to put argc, argv in the right place
byte 0x48
byte 0x81
byte 0xc4
byte 40
byte 0
byte 0
byte 0

global output_fd

goto main

function main
	argument argv2
	argument argv1
	argument argv0
	argument argc
	local input_filename
	local output_filename
	
	if argc < 3 goto default_filenames
		input_filename = argv1
		output_filename = argv2
		goto got_filenames
	:default_filenames
		input_filename = .str_default_input_filename
		output_filename = .str_default_output_filename
	:got_filenames
	
	output_fd = syscall(2, output_filename, 0x241, 420) ; 420 = octal 644
	if output_fd >= 0 goto output_file_good
	file_error(output_filename)
	:output_file_good
	exit(0)

:str_default_input_filename
	string in04a
	byte 0

:str_default_output_filename
	string out04a
	byte 0

function file_error
	argument name
	fputs(2, .str_file_error)
	fputs(2, name)
	fputc(2, 10)
	exit(1)
	
:str_file_error
	string Error opening file:
	byte 32
	byte 0


; returns a pointer to a null-terminated string containing the number given
function itos
	global 32 itos_string
	argument x
	local c
	local p
	p = &itos_string
	p += 30
	:itos_loop
		c = x % 10
		c += '0
		*1p = c
		x /= 10
		if x == 0 goto itos_loop_end
		p -= 1
		goto itos_loop
	:itos_loop_end
	return p


; returns the number at the start of the given string
function stoi
	argument s
	local p
	local n
	local c
	n = 0
	p = s
	:stoi_loop
		c = *1p
		if c < '0 goto stoi_loop_end
		if c > '9 goto stoi_loop_end
		n *= 10
		n += c - '0
		p += 1
		goto stoi_loop
	:stoi_loop_end
	return n


function strlen
	argument s
	local c
	local p
	p = s
	:strlen_loop
		c = *1p
		if c == 0 goto strlen_loop_end
		p += 1
		goto strlen_loop
	:strlen_loop_end
	return p - s

function fputs
	argument fd
	argument s
	local length
	length = strlen(s)
	syscall(1, fd, s, length)
	return

function puts
	argument s
	fputs(1, s)
	return

function fputn
	argument fd
	argument n
	local s
	s = itos(n)
	fputs(fd, s)
	return

function fputc
	argument fd
	argument c
	local p
	p = &c
	syscall(1, fd, p, 1)
	return

function putc
	argument c
	fputc(1, c)
	return
	
function exit
	argument status_code
	syscall(0x3c, status_code)


function syscall
	; I've done some testing, and this should be okay even if
	; rbp-56 goes beyond the end of the stack.
	; mov rax, [rbp-16]
	byte 0x48
	byte 0x8b
	byte 0x85
	byte 0xf0
	byte 0xff
	byte 0xff
	byte 0xff
	; mov rdi, rax
	byte 0x48
	byte 0x89
	byte 0xc7
	
	; mov rax, [rbp-24]
	byte 0x48
	byte 0x8b
	byte 0x85
	byte 0xe8
	byte 0xff
	byte 0xff
	byte 0xff
	; mov rsi, rax
	byte 0x48
	byte 0x89
	byte 0xc6
	
	; mov rax, [rbp-32]
	byte 0x48
	byte 0x8b
	byte 0x85
	byte 0xe0
	byte 0xff
	byte 0xff
	byte 0xff
	; mov rdx, rax
	byte 0x48
	byte 0x89
	byte 0xc2
	
	; mov rax, [rbp-40]
	byte 0x48
	byte 0x8b
	byte 0x85
	byte 0xd8
	byte 0xff
	byte 0xff
	byte 0xff
	; mov r10, rax
	byte 0x49
	byte 0x89
	byte 0xc2
	
	; mov rax, [rbp-48]
	byte 0x48
	byte 0x8b
	byte 0x85
	byte 0xd0
	byte 0xff
	byte 0xff
	byte 0xff
	; mov r8, rax
	byte 0x49
	byte 0x89
	byte 0xc0
	
	; mov rax, [rbp-56]
	byte 0x48
	byte 0x8b
	byte 0x85
	byte 0xc8
	byte 0xff
	byte 0xff
	byte 0xff
	; mov r9, rax
	byte 0x49
	byte 0x89
	byte 0xc1
	
	; mov rax, [rbp-8]
	byte 0x48
	byte 0x8b
	byte 0x85
	byte 0xf8
	byte 0xff
	byte 0xff
	byte 0xff
	
	; syscall
	byte 0x0f
	byte 0x05
	
	return