Randomness

antix · December 2017

How can I make my random number sequence persistent between games?

I am making something that is procedurally generated using a fixed random seed. This is fine but if the player exits the game... how do I make the random sequence continue when they next load the game?

There doesn't seem to be any way to save the current state of Core.random

hgy29 · December 2017

Couldn’t you just save the current seed to a file ? core.randomSeed() shall return the current seed.

antix · December 2017

Well that's an easy solution, thanks. Reference guide does not say that it will return the current seed

SinisterSoft · December 2017

That's odd, the pdf does...

antix · December 2017

So how does Core.randomSeed() actually work?

seed = 12345678
 
Core.randomSeed(0, seed)
print("random seed = ", Core.randomSeed())
 
local function advance() 
  seed = Core.randomSeed()
  print("advance using", seed)
end
 
stage:addEventListener(Event.KEY_DOWN, function(event) if event.keyCode == KeyCode.SPACE then advance() end end)

Running the code above I get the following results...
random seed = 12345678
advance using 13956884
advance using 14019841
advance using 14081215
advance using 14123875
advance using 14154412
advance using 14187182
advance using 14207933
advance using 14227556
advance using 14247235

Which seems to be terribly wrong in my mind because all I am attempting to do in advance() is get the current random seed. If that's syntactically correct then why am I getting different numbers when I haven't even called Core.random() at all?

It seems like it is counting up like something is adding to it constantly.

antix · December 2017

SinisterSoft said:
That's odd, the pdf does...

That's odd because the reference online does not. That's truly random :bz

oleg · December 2017

 math.randomseed(1234)
 print(math.random(), math.random(), math.random())
 
  math.randomseed(1234)
 print(math.random(), math.random(), math.random())
 
 
  print(Core.randomSeed(0,1234),Core.random(),Core.random())
    print(Core.randomSeed(0,1234),Core.random(),Core.random())

newfile.lua is uploading.
Uploading finished.
0.74087692971382 0.21453485694459 0.33819583400069
0.74087692971382 0.21453485694459 0.33819583400069

69342833 0.19151945016347 0.49766366626136
-2034653606 0.19151945016347 0.49766366626136

hgy29 · December 2017

When you call Core.randomSeed without giving it a new seed, it uses the current time as the new seed, that’s why you see it incrementing

antix · December 2017

@oleg, interesting that math.random works as expected and Core.random does not.

oleg · December 2017

antix said:
@oleg, interesting that math.random works as expected and Core.random does not.

 Core.randomSeed(0,1234)
 
  print(Core.random(),Core.random())
   Core.randomSeed(0,1234)
 
  print(Core.random(),Core.random())

0.19151945016347 0.49766366626136
0.19151945016347 0.49766366626136

antix · December 2017

@oleg yes I see it's making the same number but if I use Core.randomSeed() it gives the wrong number, which is the seed I am trying to save.

I would think that Core.randomSeed() should always return the correct seed, not something that seems, well, random.

oleg · December 2017

here is your example-everything works

seed = 12345678
 
Core.randomSeed(0, seed)
print("random seed = ", Core.random())
 
local function advance() 
	Core.randomSeed(0, seed) 
  seed = Core.random()
  print("advance using", seed)
end
 
stage:addEventListener(Event.KEY_DOWN, function(event) if event.keyCode == KeyCode.SPACE then advance() end end)

antix · December 2017

@oleg, nope, that is not working. It does not get the actual seed which is what I want to save and reload in subsequent games, it just creates a random number between 0 and 1.

oleg · December 2017

I do not understand what you want
save the seed = 12345678

antix · December 2017

During the game I call Core.random(0) to get random numbers between 0 and 1.
Internally this modifies the seed (I think).
I call Core.randomSeed() to get the seed when I want to save it.

The problem is that Core.randomSeed() does not return the actual seed, instead it seems to be returning something completely random, which is not what I require.

I hope that makes it a bit clearer

antix · December 2017

hgy29 said:
When you call Core.randomSeed without giving it a new seed, it uses the current time as the new seed, that’s why you see it incrementing

Ahh I see now. So that's then totally useless for me

I want to save the state of the random number generator so it can be used on next program load.

I'll just not use it and find another solution. In future it might be good to have such a feature though

hgy29 · December 2017

I don’t understand why it is useless. Even if you pass it a new random seed of your own or leave it use time as new seed, the function returns you the old current seed, which is what you want, no ?

oleg · December 2017

if I understood correctly

 seed=123
 
	  Core.randomSeed(0, seed) 
 for i=1,3 do
 --sequence
 print( Core.random())
 
 end
 --save
    seed=123
 ----------------------------
 --extend the sequence
 Core.randomSeed(0, seed)
 
--skip past sequence
 for i=1,3do
  Core.random()
  end
 
  --extend the sequence
 for i=1,5 do
 print( Core.random())
 
 end
 
 
 --test
 print("---------------------------------------")
   Core.randomSeed(0, 123) 
 for i=1,8 do
 print( Core.random())
 
 end

antix · December 2017

hgy29 said:
I don’t understand why it is useless. Even if you pass it a new random seed of your own or leave it use time as new seed, the function returns you the old current seed, which is what you want, no ?

Let me try to explain as best I am able...

- I am making a game where each level is procedurally generated.
- I am using the new Core.random system so that the generated results are the same for all devices.. so if I have a random seed of 1234 then on Android, IOS, and Win32 I will generate the same level on all platforms.
- The game never ends so when the player leaves the game it saves the random state.
- When the game is run again it loads the saved random state and continues generating random levels from where it left off.
- Using this system the game is the same on all platforms and the levels generated are all the same, between game sessions.

So a player who played 50 sessions and made it to level 1000 on IOS sees exactly the same level as a player who played on Android for 5 sessions and reached level 1000.

Now if the random seed that is returned by Core.randomSeed() is a time stamp then all subsequent games will differ wildly because depending on when the game was exited on any particular device.. the randomSeed returned by Core.randomSeed() will be different.

Am I correct then at saying this is useless (not going to work) for me? or am I really not getting the point?

hgy29 · December 2017

You misunderstood what Core.randomSeed actually does.
It has two functions:
1°) it returns you the current seed (so that you can resume an ongoing rrandom sequence)
2°) it allows you to set a new seed

both functions are executed at the same time during the call:

oldSeed=Core.randomSeed(0,newSeed)

if you don't specify a newSeed (or leave it nil), then os.timer() is used as the new seed. This has no effect on the oldSeed.

So you can still use the oldSeed, save it, and resume your game with Core.randomSeed(0,oldSeed).

You see ?

totebo · December 2017

Reading through this I thought there might be something I'm missing, because I plan to use Core.random myself to generate persistent procedural levels. I tested it quickly, and it works great.

This saves and increments a seed, producing the same random number on any device (well, I tested it on Mac and Android, try it to see if it works for you!).

	local seed
 
	-- Load seed if available
	local seed_filename = "|D|saved_seed.txt"
	local file = io.open( seed_filename, "r")
	if file then
		local str = file:read("*all") 
		seed = tonumber(str)
		file:close()
	else
		seed = 0
	end
 
	-- Use seed
	Core.randomSeed( 0, seed )
	local random_number = Core.random()	
	print( "Seed: " .. seed .. " Random number: " .. random_number )
 
	-- Increment seed
	seed += 1
 
	-- Save seed
	local file = io.open( seed_filename, "w")
	file:write( seed )
	file:close()

Spitting out this:

Uploading finished.
Seed: 0 Random number: 0.54881350230426
Uploading finished.
Seed: 1 Random number: 0.41702199843712
Uploading finished.
Seed: 2 Random number: 0.43599490262568

antix · December 2017

@hgy29 yes I totally mis-understood how it work it seems

@totebo that's pretty cool, just adjusting the seed by one. That would work but it does not save the true state of the random number generator.

I know I'm being a bit "picky" but I want to save the state of the original seed as it unfolds. To this end I am looking for a pure lua based generator where I can get and set it's state as I please.

Sorry to all that I confused

hgy29 · December 2017

@antix, I think you are confused by the fact that running Core.randomSeed() repeatedly changes the current seed: it is true, but not an issue since what you want is the first result. You don't care if the seed is changed afterwise since you don't intend to generate more random numbers afterward.

Try this:

function getSeed()
 local seed=Core.randomSeed(0) --Grab current seed and sets a new time based seed
 Core.randomSeed(0,seed) -- Reset the old seed, just in case
 return seed
end
 
function setSeed(s)
 Core.randomSeed(0,s)
end

antix · December 2017

@hgy29, I now get how it works, it just doesn't work how I want it to

hgy29 · December 2017

Yes, this is because random generator states are not the seed. Basically the seed is expanded to a bigger structure on which the random generator works. Core.randomSeed return value is an extract of the state which could be reused to restart the generator in a state not too far than what is was. There is no guarantee that it will give the same sequence as if you let the initial random generator continue.

SinisterSoft · December 2017

There is something pretty important you need to remember when dealing with a random number returned between 0 and 1, because of floating point differences they may actually be different between devices.

If you want things to be exactly the same between devices then use random integers instead.

SinisterSoft · December 2017

It is possible for a less random number function to be added that does return the seed in a 32 bit number. The core.random system has a parameter to pick a different random generator.

antix · December 2017

SinisterSoft said:
There is something pretty important you need to remember when dealing with a random number returned between 0 and 1, because of floating point differences they may actually be different between devices.

If you want things to be exactly the same between devices then use random integers instead.

@SinisterSoft that's very handy to know. So I suppose I can get a random number from 1 to 10,000 and then divide that by 10,000 which should produce exact results across platforms right? Or does that still allow for floating point errors?

SinisterSoft · December 2017

No - any floating point between systems could be different (slightly). The random function (I think) keeps everything as integer anyway until it's given to the user - so they won't be wildly out over time.

antix · December 2017

@SinisterSoft okay got it. I checked the random code that I found on github and it does seem to use integers internally and then spits back floating points when required.

So now I have a basic random number generator that can persist between sessions I'm happy. This is it if anybody might find it useful..

--[[
 
Found this code here...
<a href="https://github.com/linux-man/randomlua" rel="nofollow">https://github.com/linux-man/randomlua</a>
 
 
Ripped it up, retaining MWC stuff, and added some 
bits to allow getting and setting the random state
 
 
Original credits...
RandomLua v0.3.2
Pure Lua Pseudo-Random Numbers Generator
Under the MIT license.
copyright(c) 2016 Caldas Lopes
 
--]]
 
Random = Core.class()
 
function Random:init(seed)
  seed = seed or os.time()
  self.a, self.c, self.m = 214013, 2531011, 0x100000000 -- from MVC
	self.ic = self.c
  self:randomSeed(seed)
end
 
function Random:random(a, b)
  local floor = math.floor
	local m = self.m
	local t = self.a * self.seed + self.c
	local y = t % m
	self.seed = y
	self.c = floor(t / m)
	if not a then return y / 0x100000000
	elseif not b then
		if a == 0 then return y
		else return 1 + (y % a) end
	else
		return a + (y % (b - a + 1))
	end
end
 
function Random:randomSeed(seed)
	self.c = self.ic
	self.seed = seed % 0x100000000
end
 
function Random:getState()
  return {
    seed  = self.seed,
    a     = self.a,
    c     = self.c,
    m     = self.m,
    ic    = self.ic,
  }
end
 
function Random:setState(state)
    self.seed  = state.seed
    self.a     = state.a
    self.c     = state.c
    self.m     = state.m
    self.ic    = state.ic
end
 
function Random:dumpState()
  print("Random State")
  print("seed " .. self.seed)
  print("a    " .. self.a)
  print("c    " .. self.c)
  print("m    " .. self.m)
  print("ic   " .. self.ic)
end

SinisterSoft · December 2017

self.c = floor(t / m)

can be changed to

self.c = t//m

faster...

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