-- ilo.lua
-- Partially derived from Ngaro in Lua
-- Copyright (c) 2010 - 2023, Charles Childers
--
-- This is only tested on Lua 5.4 and requires 32-bit
-- integers. (set `#define LUA_32BITS 1` in luaconf.h when
-- building Lua)

-- Variables
local ip = 0                -- instruction pointer
local sp = 0                -- stack pointer
local rp = 0                -- return pointer
local stack = {}            -- data stack
local address = {}          -- return stack
local memory = {}           -- simulated ram

-- Support Code
local function file_size(filename)
  local fh = assert(io.open(filename, 'rb'))
  local len = assert(fh:seek('end'))
  fh:close()
  return len
end

local function constrain(n)
  return (n > 0x7FFFFFFF) and (n - 0x100000000) or n
end

local function save_image()
  local image = io.open('ilo.rom', 'wb')
  local i = 0
  while i < 65536 do
    image:write(string.pack('<i4', memory[i]))
    i = i + 1
  end
  image:close()
end

local function read_block()
  local blocks = io.open('ilo.blocks', 'rb')
  local buffer = stack[sp]
  local block = stack[sp - 1]
  sp = sp - 2
  local i = 0
  blocks:seek('set', block * 4096)
  while i < 1024 do
    memory[buffer] = string.unpack('<i4', blocks:read(4))
    buffer = buffer + 1
    i = i + 1
  end
  blocks:close()
end

local function write_block()
  local blocks = io.open('ilo.blocks', 'r+b')
  local buffer = stack[sp]
  local block = stack[sp - 1]
  sp = sp - 2
  local i = 0
  blocks:seek('set', block * 4096)
  while i < 1024 do
    local x = memory[buffer + i]
    local b4=string.char(x%256) x=(x-x%256)/256
    local b3=string.char(x%256) x=(x-x%256)/256
    local b2=string.char(x%256) x=(x-x%256)/256
    local b1=string.char(x%256) x=(x-x%256)/256
    blocks:write(b4,b3,b2,b1)
    i = i + 1
  end
  blocks:close()
end

local opcodes = {
  [0] = function() end,        -- no (nop)
  [1] = function()             -- li (lit)
    sp = sp + 1
    ip = ip + 1
    stack[sp] = memory[ip]
  end,
  [2] = function()             -- du (dup)
    sp = sp + 1
    stack[sp] = stack[sp - 1]
  end,
  [3] = function()             -- dr (drop)
    sp = sp - 1
  end,
  [4] = function()             -- sw (swap)
    local a = stack[sp]
    stack[sp] = stack[sp - 1]
    stack[sp - 1] = a
  end,
  [5] = function()             -- pu (push)
    rp = rp + 1
    address[rp] = stack[sp]
    sp = sp - 1
  end,
  [6] = function()             -- po (pop)
    sp = sp + 1
    stack[sp] = address[rp]
    rp = rp - 1
  end,
  [7] = function()             -- ju (jump)
    ip = stack[sp] - 1
    sp = sp - 1
  end,
  [8] = function()             -- ca (call)
    rp = rp + 1
    address[rp] = ip
    ip = stack[sp] - 1
    sp = sp - 1
  end,
  [9] = function()             -- cc (cond. call)
    if stack[sp - 1] ~= 0 then
      rp = rp + 1
      address[rp] = ip
      ip = stack[sp] - 1
    end
    sp = sp - 2
  end,
  [10] = function()            -- cj (cond. jump)
    if stack[sp - 1] ~= 0 then
      ip = stack[sp] - 1
    end
    sp = sp - 2
  end,
  [11] = function()            -- re (return)
    ip = address[rp]
    rp = rp - 1
  end,
  [12] = function()            -- eq (equality)
    if stack[sp - 1] == stack[sp] then
      stack[sp - 1] = -1
    else
      stack[sp - 1] = 0
    end
    sp = sp - 1
  end,
  [13] = function()            -- ne (inequality)
    if stack[sp - 1] == stack[sp] then
      stack[sp - 1] = 0
    else
      stack[sp - 1] = -1
    end
    sp = sp - 1
  end,
  [14] = function()            -- lt (less than)
    if stack[sp - 1] < stack[sp] then
      stack[sp - 1] = -1
    else
      stack[sp - 1] = 0
    end
    sp = sp - 1
  end,
  [15] = function()            -- gt (greater than)
    if stack[sp - 1] > stack[sp] then
      stack[sp - 1] = -1
    else
      stack[sp - 1] = 0
    end
    sp = sp - 1
  end,
  [16] = function()            -- fe (fetch)
    stack[sp] = memory[stack[sp]]
  end,
  [17] = function()            -- st (store)
    memory[stack[sp]] = stack[sp - 1]
    sp = sp - 2
  end,
  [18] = function()            -- ad (add)
    stack[sp - 1] = stack[sp - 1] + stack[sp]
    sp = sp - 1
  end,
  [19] = function()            -- su (subtract)
    stack[sp - 1] = stack[sp - 1] - stack[sp]
    sp = sp - 1
  end,
  [20] = function()            -- mu (multiply)
    stack[sp - 1] = stack[sp - 1] * stack[sp]
    sp = sp - 1
  end,
  [21] = function()            -- di (divide & remainder)
    local b = stack[sp]
    local a = stack[sp - 1]
    local x = math.abs(b)
    local y = math.abs(a)
    local q = constrain(y // x)
    local r = constrain(y % x)
    if a < 0 and b < 0 then
      r = r * -1
    elseif a > 0 and b < 0 then
      q = q * -1
    elseif a < 0 and b > 0 then
      r = r * -1
      q = q * -1
    end
    stack[sp] = q
    stack[sp - 1] = r
  end,
  [22] = function()            -- an (and)
    stack[sp - 1] = stack[sp - 1] & stack[sp]
    sp = sp - 1
  end,
  [23] = function()            -- or (or)
    stack[sp - 1] = stack[sp - 1] | stack[sp]
    sp = sp - 1
  end,
  [24] = function()            -- xo (xor)
    stack[sp - 1] = stack[sp - 1] ~ stack[sp]
    sp = sp - 1
  end,
  [25] = function()            -- sl (shift left)
    stack[sp - 1] = stack[sp - 1] << stack[sp]
    sp = sp - 1
  end,
  [26] = function()            -- sr (shift right)
    stack[sp - 1] = stack[sp - 1] >> stack[sp]
    sp = sp - 1
  end,
  [27] = function()            -- cp (compare)
    local a = stack[sp]       -- length
    local b = stack[sp - 1]   -- dest
    local c = stack[sp - 2]   -- source
    local d = -1              -- flag
    sp = sp - 3
    while a > 0 do
      if memory[b] ~= memory[c] then
        d = 0
      end
      a = a - 1
      b = b + 1
      c = c + 1
    end
    sp = sp + 1
    stack[sp] = d
  end,
  [28] = function()            -- cy (copy)
    local a = stack[sp]       -- length
    local b = stack[sp - 1]   -- dest
    local c = stack[sp - 2]   -- source
    sp = sp - 3
    while a > 0 do
      memory[b] = memory[c]
      a = a - 1
      b = b + 1
      c = c + 1
    end
  end,
  [29] = function()    -- io
    local d = stack[sp]
    sp = sp - 1
    if d == 0 then
      io.write(string.char(stack[sp]))
      sp = sp - 1
    elseif d == 1 then
      sp = sp + 1
      stack[sp] = string.byte(io.read(1))
    elseif d == 2 then
      read_block()
    elseif d == 3 then
      write_block()
    elseif d == 4 then
      save_image()
    elseif d == 5 then
      load_image("ilo.rom")
      ip = -1
      sp = 0
      rp = 0
    elseif d == 6 then
      ip = 65536
    elseif d == 7 then
      sp = sp + 1
      stack[sp] = sp - 1
      sp = sp + 1
      stack[sp] = rp
    end
  end
}

-- -------------------------------------------------------------
-- process opcodes
local function process_opcode(opcode)
  if opcode == 0 then return end -- skip NOP instructions
  local op_fn = opcodes[opcode]
  if op_fn then op_fn() end
end

local function process_opcodes()
  local opcode = memory[ip]
  process_opcode(opcode     & 0xFF)
  process_opcode(opcode>>8  & 0xFF)
  process_opcode(opcode>>16 & 0xFF)
  process_opcode(opcode>>24 & 0xFF)
end

-- Load image into memory
-- \ cells = size of image file (in cells)
-- \ image = pointer to retroImage file
local function load_image(file)
  local cells = file_size(file) / 4
  local image = io.open(file, 'rb')
  local i = 0
  while i < cells do
    memory[i] = string.unpack('<i4', image:read(4))
    i = i + 1
  end
  image:close()
  while i < 65536 do
    memory[i] = 0
    i = i + 1
  end
  i = 0
  while i < 33 do
    stack[i] = 0
    address[i] = 0
    i = i + 1
  end
  while i < 257 do
    address[i] = 0
    i = i + 1
  end
end

local function dump_stack()
  while sp > 0 do
    print(stack[sp])
    sp = sp - 1
  end
end

local function process_instructions()
  while ip < 65536 do
    process_opcodes()
    ip = ip + 1
  end
end

local function main()
  load_image("ilo.rom")
  process_instructions()
  dump_stack()
end

main()