fix slime chunks algorithm

[asquared31415]

The old algorithm was incorrectly using integer literals in two places instead of long literals. This caused it to incorrectly handle certain seeds. I also took the liberty of making the code exactly match the reference implementation on the wiki using hex literals and casts, just to be sure it was completely identical.

[wlhlm]

Hmm, it's better to look at the decompiled Minecraft source rather than the wiki. Here is the snippet, defined in net.minecraft.entity.monster.EntitySlime#getCanSpawnHere:

 public boolean getCanSpawnHere() {
    Chunk chunk = this.worldObj.getChunkFromBlockCoords(MathHelper.floor_double(this.posX), MathHelper.floor_double(this.posZ));
    // ...
    if (this.rand.nextInt(10) == 0 && chunk.getRandomWithSeed(987234911L).nextInt(10) == 0 && this.posY < 40.0D) {
        return super.getCanSpawnHere();
    }
    // ...
}

Here is net.minecraft.world.chunk.Chunk#getRandomWithSeed:

public Random getRandomWithSeed(long p_76617_1_) {
    return new Random(this.worldObj.getSeed() + (long)(this.xPosition * this.xPosition * 4987142) + (long)(this.xPosition * 5947611) + (long)(this.zPosition * this.zPosition) * 4392871L + (long)(this.zPosition * 389711) ^ p_76617_1_);
}

You can see the code actually casts the terms to long rather than int.

[asquared31415]

Ah interesting, it turns out that that's actually an implicit cast to long anyway, the (int) were entirely redundant. Pushed an update making the casts explicit to be more clear and silence IDE warnings.

[wlhlm]

Thanks! 👍