localize a couple more things

nn.lua

@@ -1,3 +1,4 @@
+local assert = assert
 local ceil = math.ceil
 local cos = math.cos
 local exp = math.exp

smb.lua

@@ -1,6 +1,16 @@
 -- disassembly used for reference:
 -- https://gist.githubusercontent.com/1wErt3r/4048722/raw/59e88c0028a58c6d7b9156749230ccac647bc7d4/SMBDIS.ASM
 
+local band = bit.band
+local floor = math.floor
+local emu = emu
+local gui = gui
+
+local util = require("util")
+local R = memory.readbyteunsigned
+local W = memory.writebyte
+local function S(addr) return util.signbyte(R(addr)) end
+
 local rotation_offsets = { -- FIXME: not all of these are pixel-perfect.
     0, -40, -- 0x00
     6, -38,
@@ -36,11 +46,6 @@ local rotation_offsets = { -- FIXME: not all of these are pixel-perfect.
     -8, -38,
 }
 
-local util = require("util")
-local R = memory.readbyteunsigned
-local W = memory.writebyte
-local function S(addr) return util.signbyte(R(addr)) end
-
 -- TODO: reinterface to one "input" array visible to main.lua.
 local sprite_input = {}
 local tile_input = {}
@@ -48,9 +53,6 @@ local extra_input = {}
 
 local overlay = false
 
-local band = bit.band
-local floor = math.floor
-
 local function get_timer()
     return R(0x7F8) * 100 + R(0x7F9) * 10 + R(0x7FA)
 end