FCEUX LUA RNG Sample Testing Script

-- FCEUX LUA RNG Sample Testing Script
-- by ZeroNoin


-- This LUA script is heavily based on script by Omnigamer found here:
-- http://pastebin.com/Qv6sw2j7
-- This FCEUX script takes an RNG address and sets it to various values at the start of savestate loads.
-- It counts the desired results found in other addresses from an event after the savestate load.
-- Pause the emulator just before the RNG event, then run this script via File > Lua, then unpause the emulator.
-- It can be difficult to find RNG in game assembly, and the RNG can shuffle in strange ways, so sample testing can help.
-- The values given here were used in Blaster Master to test H drop rates.


-- RNG RAM address, addresses showing result of RNG, number of result addresses, and value compared for RNG success.
-- In the case of Blaster Master, an item drop (including an H drop) is labeled with a value of 0x35.
-- There are 8 locations in the RAM where an item drop can be placed.
RNG_ADDRESS = 0x0013
RESULT_ADDRESSES = {0x0470,0x047E,0x048C,0x049A,0x04A8,0x04B6,0x04C4,0x04D2}
RESULT_VALUE = 0x35

-- Count of RNG successes, iterated value put in the RNG RAM, and length of RNG value iterations.
-- Since only one 8-bit address holds the RNG value in Blaster Master, there are 0x100 (256) possible values, 0x00 through 0xFF.
COUNT = 0
CURRENT = 0x00
ITERATIONS = 0x100

-- Frames from the loaded savestate to give for the RNG event to occur.
FRAMES = 15

-- A savestate number assigned for the test (this save is separate from normal savestate slots in the emulator).
-- The savestate must be created and stored as an object in order for this script to reference it.
-- The savestate object does not contain a savestate until one is saved in it.
SAVE_NUMBER = 1
SAVE_STATE = savestate.create(SAVE_NUMBER)
savestate.save(SAVE_STATE)

-- Variables for placement of the displayed results.
-- Pixels from the top left in X and Y distance, and pixels spacing the start of each line.
DISPLAY_X = 16
DISPLAY_Y = 32
SPACING = 8


-- Set the RNG at its specific address in the RAM to a given value.
function set_rng(value)
    memory.writebyte(RNG_ADDRESS,value)
end


-- Compare the value at a resulting address with the value considered RNG success.
function compare_result(address,value)
    if(memory.readbyte(address)==value) then
        return true
    else
        return false
    end
end


-- Check the results in the given addresses, and count the successes.
-- Output (print) successful RNG values to the emulator LUA console.
function check_result()
    for i=1,table.getn(RESULT_ADDRESSES),1 do
        if(compare_result(RESULT_ADDRESSES[i],RESULT_VALUE)) then
            COUNT = COUNT+1
            emu.print(string.upper(string.format("%02x",CURRENT)))
            break
        end
    end
end


-- Display the current results of the test in text.
-- The "O" displays wide in FCEUX, so I decided to use "0" instead.
function display_results()
    gui.text(DISPLAY_X,DISPLAY_Y,string.format("C0UNT   %3d",COUNT))
    gui.text(DISPLAY_X,DISPLAY_Y+SPACING,string.format("CURRENT %3d",CURRENT))
    gui.text(DISPLAY_X,DISPLAY_Y+SPACING+SPACING,string.format("PERCENT  %.2f%%",(COUNT/CURRENT)*100))
end


-- Advance the frames a given quantity for the event to occur.
-- Also display the status of the results on each frame.
function advance_frames(value)
    for i=0,value,1 do
        emu.frameadvance()
        display_results()
    end
end


-- Main script utilizing the above variables and functions.
-- For all the RNG values, load the savestate, set the RNG, and advance the frames a given amount for the event.
-- After the frames advance the event, check and count the result of the event in corresponding addresses in the RAM.
-- When complete, output totals to the emulator LUA console and continually advance frames and display the results.
while(CURRENT<ITERATIONS) do
    savestate.load(SAVE_STATE)
    set_rng(CURRENT)
    advance_frames(FRAMES)
    check_result()
    CURRENT = CURRENT+0x01
end
emu.print(string.format("COUNT %3d",COUNT))
emu.print(string.format("CURRENT %3d",CURRENT))
emu.print(string.format("PERCENT %.2f%%",(COUNT/CURRENT)*100))
while(true) do
    advance_frames(1)
end