px9_decomp.lua

function px9_decomp(x0,y0,src,vget,vset)
    local function vlist_val(l, val)
        local v,i=l[1],1
        while v!=val do
            i+=1
            v,l[i]=l[i],v
        end
        l[1]=val
    end

    local cache,cache_bits=0,0
    function getval(bits)
        if cache_bits<8 then
            cache_bits+=8
            cache+=@src>>cache_bits
            src+=1
        end

        cache<<=bits
        local val=cache&0xffff
        cache^^=val
        cache_bits-=bits
        return val
    end

    function gnp(n)
        local bits=0
        repeat
            bits+=1
            local vv=getval(bits)
            n+=vv
        until vv<(1<<bits)-1
        return n
    end

    local w,h_1, eb,el,pr, x,y, splen, predict = gnp"1",gnp"0", gnp"1",{},{}, 0,0, 0

    for i=1,gnp"1" do
        add(el,getval(eb))
    end

    for y=y0,y0+h_1 do
        for x=x0,x0+w-1 do
            splen-=1

            if(splen<1) then
                splen,predict=gnp"1",not predict
            end

            local a=y>y0 and vget(x,y-1) or 0
            local l=pr[a] or {unpack(el)}
            pr[a]=l
            local v=l[predict and 1 or gnp"2"]
            vlist_val(l, v)
            vlist_val(el, v)
            vset(x,y,v)
        end
    end
end