# assembler.rb

# # # REGISTER NAMES # # #
def r0() 0 end # zero
def at() 1 end # assembler temporary

# subroutine return values, may be changed by subroutines
def v0() 2 end ; def v1() 3 end

# subroutine arguments, may be changed by subroutines
def a0() 4 end ; def a1() 5 end
def a2() 6 end ; def a3() 7 end

# temporaries, may be changed by subroutines
def t0() 8 end ; def t1() 9 end
def t2() 10 end ; def t3() 11 end
def t4() 12 end ; def t5() 13 end
def t6() 14 end ; def t7() 15 end

# static variables, must be saved by subs
def s0() 16 end ; def s1() 17 end
def s2() 18 end ; def s3() 19 end
def s4() 20 end ; def s5() 21 end
def s6() 22 end ; def s7() 23 end

# temporaries, may be changed by subroutines
def t8() 24 end ; def t9() 25 end

# reserved for kernel, detroyed by some irq handlers
def k0() 26 end ; def k1() 27 end

def gp() 28 end # global pointer, rarely used (we can use this to reffer to a struct or smtn)
def sp() 29 end # stack pointer
def fp() 30 end # frame pointer
def ra() 31 end # return address

class Assembler
	def initialize(base, size)
		@base_addr = base
		@file_size = size

		# moar vars defined in assemble()
	end

	def inspect
		"(Assembler base_addr:0x#{@base_addr.to_s 16} file_size:0x#{@file_size.to_s 16})"
	end

	def label(l)
		l = l.to_s

		@sub_labels[l] = {} if not @sub_labels.member?(l)
		@last_label_subs = @sub_labels[l]

		return if @first_pass == false
		raise "error redefinition of label #{l}" if @labels.member?(l)
		@labels[l] = @bytes.length + @base_addr
	end

	def sub_label(l)
		return if @first_pass == false
		l = l.to_s
		raise "error redefinition of sub_label #{l}" if @last_label_subs.member?(l)
		@last_label_subs[l] = @bytes.length + @base_addr
	end

	def method_missing(m, *args, &block)
		return 0 if @first_pass
		if @last_label_subs[m.to_s] then
			return @last_label_subs[m.to_s]
		elsif @labels.member?(m.to_s) then # if m.to_s[0, 2] == "l_" then
			return @labels[m.to_s] #return @labels[m.to_s[2..]] if @labels.member?(m.to_s[2..])
			#raise "label doesn't exist #{m.to_s}"
		else
			super
		end
	end

	def assemble(source)
		@first_pass = true
		@labels = {}
		@bytes = []
		@sub_labels = {}
		@last_label_subs = {}
		binding.eval source

		@first_pass = false
		@bytes = []
		@last_label_subs = {}
		binding.eval source

		puts "assembled 0x#{@bytes.length.to_s 16} (#{@bytes.length}) bytes"
		raise "CODE IS GREATER THAN FILESIZE" if @bytes.length > @file_size
		zero_fill @file_size - 1

		return @bytes
	end

	def zero_fill(pos)
		while (@bytes.length <= pos) do
			@bytes.push(0)
		end
	end
	
	def word(i)
		@bytes.push((i & 0x000000ff),
			(i & 0x0000ff00) >> 8,
			(i & 0x00ff0000) >> 16,
			(i & 0xff000000) >> 24)
	end
	
	def string(s)
		@bytes.push *s.bytes
		@bytes.push 0 # null terminate
		while ((@bytes.length % 4) != 0) do
			@bytes.push 0
		end
	end


	# # # INSTRUCTIONS # # #

	# ops should always be in format of
	# [src] [args] -> [dest]

	def jmp(addr)
		# TODO: this probs wont show up since we have < 3mb of ram but
		# we can't jump to an address with a different 4 most significant bits
		raise "jmp addr must be 4 byte aligned" if addr % 4 != 0
		op = 0b0000_1000_0000_0000_0000_0000_0000_0000
		op = op | ((addr >> 2) & 0b11_11111111_11111111_11111111)
		word op
	end

	def jal(addr)
		# TODO: same problem as jmp
		raise "jmp addr must be 4 byte aligned" if addr % 4 != 0
		op = 0b0000_1100_0000_0000_0000_0000_0000_0000
		op = op | ((addr >> 2) & 0b11_11111111_11111111_11111111)
		word op
	end

	# load upper immediate
	# NOTE: val will be shifted left by 16
	def lui(val, dest)
		#      oooooo ----- ddddd iiiiiiiiiiiiiiii
		op = 0b001111_00000_00000_0000000000000000
		op |= 0xffff & val
		op |= (0b11111 & dest) << 16
		word op
	end

	# shift right logical
	def srl(src, amt, dest)
		#      oooooo ----- sssss ddddd hhhhh oooooo
		op = 0b000000_00000_00000_00000_00000_000010
		op |= (src & 0b11111) << 16
		op |= (amt & 0b11111) << 6
		op |= (dest & 0b11111) << 11
		word op
	end

	# or immediate
	def ori(src, bits, dest)
		#      oooooo sssss ddddd iiiiiiii iiiiiiii
		op = 0b001101_00000_00000_00000000_00000000
		op |= (src & 0b11111) << 21
		op |= (bits & 0xffff)
		op |= (dest & 0b11111) << 16
		word op
	end

	# store word
	# NOTE: this doesn't work unaligned
	def sw(src, offset, dest)
		#      oooooo ddddd sssss iiiiiiii iiiiiiii
		op = 0b101011_00000_00000_00000000_00000000
		op |= (src & 0b11111) << 16
		op |= (offset & 0xffff)
		op |= (dest & 0b11111) << 21
		word op
	end

	# add immediate unsigned
	def addiu(src, val, dest)
		#      oooooo sssss ddddd iiiiiiii iiiiiiii
		op = 0b001001_00000_00000_00000000_00000000
		op |= (src & 0b11111) << 21
		op |= (val & 0xffff)
		op |= (dest & 0b11111) << 16
		word op
	end

	# add immediate
	def addi(src, val, dest)
		#      oooooo sssss ddddd iiiiiiii iiiiiiii
		op = 0b001000_00000_00000_00000000_00000000
		op |= (src & 0b11111) << 21
		op |= (val & 0xffff)
		op |= (dest & 0b11111) << 16
		word op
	end

	# jump register
	def jr(reg)
		#      oooooo rrrrr ----- ----- ----- oooooo
		op = 0b000000_00000_00000_00000_00000_001000
		op |= (reg & 0b11111) << 21
		word op
	end

	# TODO: actually encode "comment" argument
	def syscall(comment)
		#      iiiiii ccccc ccccc ccccc ccccc iiiiii
		op = 0b000000_00000_00000_00000_00000_001100
		word op
	end

	# TODO: expose the return address storage register
	# NOTE: cannot use the same register for both operands
	def jalr(reg)
		# jumps to addr in j and stores return adr in r
		#      iiiiii jjjjj ----- rrrrr ----- iiiiii
		op = 0b000000_00000_00000_00000_00000_001001
		op |= (reg & 0b11111) << 21
		op |= (ra) << 11 # ra
		word op
	end

	# # # PSEUDO-INSTRUCTIONS # # #
	def nop
		word 0x00000000
	end

	# load immediate
	# TODO: check if we need to use 1 or 2 ops and output that
	def li(dest, val)
		lui val >> 16, dest
		ori dest, val, dest
	end

end


# # # CONSTANTS # # #
base_addr = 0x80010000 # 0x10000 # 0x80010000
file_size = 0x800 * 3

f = File.new "exe-header.asm.rb", "r"
exe_header = Assembler.new(base_addr, 0x800).assemble f.read
# puts f.path
f.close

f = File.new "main.asm.rb", "r"
binary = Assembler.new(base_addr, file_size).assemble f.read
f.close

f = File.new "LOADTHIS.EXE", "wb"
f.write exe_header.pack("C*")
f.write binary.pack("C*")
f.close