Saving the state of a random seed generator

[Madrayken]

Hi folks,
I'm writing a turn-based adventure game which uses random seeds extensively.
I'd like to save the state of the random generator when the player saves, so that there's no difference between saving and loading and continuing to play the game.

So far I've been using a horrible table lookup of 2000 random numbers to do this, but there are huge issues with this solution. Anyone else have a favourite method of saving the state of love.math.random?

[pgimeno]

Rather than love.math.random, you can use a RandomGenerator object, which has a RandomGenerator:getState() method.

Note it's only guaranteed to work within the same major version of Löve.

[Madrayken]

Does this mean it’s due for depreciation?

[pgimeno]

No, love.math.random is provided for the convenience of not having to create an object, for those who just want random numbers and no advanced features. It was introduced at the same time as the RandomGenerator object IIRC.

The pseudorandom number generator used internally may change between major versions. The developers make no guarantees that the same generator will be kept from one major version to another; they only guarantee that it won't change between minor or patch versions. And if the random number generator changes, it's likely that the state save format changes as well.

I think such a change happened in 0.10.0:

• Updated love.math.setRandomSeed and RandomGenerator:setSeed to produce better results for the first few random() calls.
• Updated love.math.random and RandomGenerator:random to produce slightly better results in general.

And another in 11.0:

• Updated love.math.random to have improved numeric distribution.

(note however that I get the same numbers for the same seed in 11.3 and 0.10.2, so it's unlikely that the state format has changed between 0.10 and 11.0).

I don't know if any of these changes came with a change of the internal state format.

[ReFreezed]

Rather than love.math.random, you can use a RandomGenerator object, which has a RandomGenerator:getState() method.

The equivalent function for love.math.random is love.math.getRandomState. love.math.random simply uses a hidden RandomGenerator object that LÖVE automatically creates at startup.

[pgimeno]

Oops, I missed that one, sorry.

[Mokona]

Have you tried to use the last number generated as the seed ?

[pgimeno]

Have you tried to use the last number generated as the seed ?

Not a good idea. If the last number generated was in the range 0 to 1, for example, that will only result in two possible sequences after restoring.

That method only works when drawing full-range integers from a generator that consists of a pseudorandom cyclic permutation, and with a state space that fits in the integer (these two conditions typically happen in linear-congruential generators, like those in some old C or Pascal libraries). Löve's built-in generator's state space is 64 bits IIRC, which don't fit in the 53 bits a double can hold.

[AuahDark]

If we're gonna change the RNG algorithm in next major release (slime said if he's gonna rework the LOVE RNG, he'll use PCG), maybe we'll allow user to select the RNG algorithm and "pcg" is default (in this case) and "xorshift" to use the older RNG.