Majora's Mask - instruction_counter

-- instruction_counter.lua
--
-- This script is designed to run on Majora's Mask (U), however can easily be
-- changed to run on (J) by making changes to addresses/sizes.
--
-- This script is used to find what the values of the "instruction counter" gets
-- overwritten to given specific indices. The instruction counter getting
-- written allows for easily manipulatable text overflow options.
--
-- Author: @Faschz
-- Created: May 5th, 2019

-- All specific to the current language/version of the game.
STRING_BASE = 0x1D0714  -- Address to the start of the table for the strings.
LENGTH_BASE = 0x1D07C4  -- Address to the start of the table for the lengths.
ENTRANT_SIZE = 16       -- Size of each entrant of the string table.

-- The amount of bytes offset from the start of the written string in order to
-- reach the specific addresses.
INSTRUCTION_OFFSET = 191
PAUSE_OFFSET = 1767

-- The calculated required length to overwrite the addresses from the text
-- overflow glitch without the use of the instruction counter.
REQUIRED_LENGTH = INSTRUCTION_OFFSET + 1 -- Address is a short, so add 1

file = io.open("instruction_counter.txt", "w")

-- The address for the index is a signed short, so the value range is as follows
-- for RTA viable indices.
for index=-300, 300 do
    length = mainmemory.read_s16_be(LENGTH_BASE + 2*index)

    -- Check if the length is high enough to overwrite the "instruction counter"
    -- while also being low enough as to not overwrite the menu type and debug
    -- menu short
    if (length >= REQUIRED_LENGTH and length < PAUSE_OFFSET) then
        instruction = mainmemory.read_u16_be(STRING_BASE + ENTRANT_SIZE*index +
                                                INSTRUCTION_OFFSET)
        file:write(index.." --- "..length.." --- "..instruction.."\n")
    end
end

file:close()

print("Finished instruction_counter.lua!")