Eniko Collatz Fizzle Fade, Pico 8 implementation

collatz.lua

seed = 38

function txp1()
    if seed == 1 then
        return seed
    elseif seed % 2 == 0 then
        seed /= 2
    else
        seed = seed * 3 + 1
    end
    -- keep seed positive if overflow occurs
    -- this just masks off the sign bit in pico 8
    seed = seed & 0x7fff
    return seed
end

c = 8

function _init()
    cls(0)
end

function _draw()
    local step = txp1()
    if step == 1 then
        cls(c)
        return
    end
    
    local x, y = 0, 0

    if step == 4 then
        step = 3
    elseif step == 2 then
        step = 3
        x = 2
    elseif step % 2 == 0 then
        step += 1
    end
    
    while y < 128 do
        x += step
        if x >= 128 then
            local rows = flr(x / 128)
            y += rows
            x = x % 128
        end
        pset(x, y, c)
    end
end