Junichi Masuda is a Japanese video game composer, director, designer, producer, singer, programmer and trombonist, best known for his work in the Pokémon franchise. He is a member of the Game Freak board of directors, and has been employed at the company since 1989 when he founded it alongside Satoshi Tajiri and Ken Sugimori.

In the pokemon games, many of the interactions in the game are decided by the output of a pseudo-random number generator, or pRNG. For example, when the player encounters a pokemon, its stats are determined by the state of the pRNG.

In the generation 3 games (R/S/E/Fr/Lg), the game displays roughly 60 frames/second, and the state of the pRNG is said to be "advanced" every frame. This means if the player knows

• the initial seed passed to the pRNG
• the mechanics behind how the pRNG is advanced
• how the numbers outputted by the pRNG are converted into pokemon stats

Then the user can find a frame which will produce a desireable pokemon, wait for the amount of time before the desired frame occurs, then encounter the desired pokemon.

masuda is a library written in rust which implements the behavior of the random number generator used in the pokemon games. Specifically, it provides an implementation of a linear congruential generator which produces a sequence of pseudo random numbers.

Try running the examples to see it in action

cargo run --example ten_frames generates 10 frames and the pokemon generated on those frames

cargo run --example is_shiny finds the shiny frames in the first 100000 frames for the given tid/sid and displays them

most usages of this lib will probably look something like this:

// create an searcher instance with game, method, and max frames
let mut searcher = Searcher::new(Game::Emerald, Method::One, 1000000);
// create a profile with a tid and an sid
let profile = Profile::new(10101, 12345);
// create a filter for the attributes you care about
// in this example, let's look for a 31/31/x/x/x/31 Jolly spread
let filter = Filter::new(&profile)
        .with_stat(StatFilter::HP(StatComparison::EqualTo(31)))
        .with_stat(StatFilter::Attack(StatComparison::EqualTo(31)))
        .with_stat(StatFilter::Speed(StatComparison::EqualTo(31)))
        .with_nature(Nature::Jolly); 

for result in searcher.search(Some(Filter)) {
    println("{:?}", result);
}