ptrsave

local function BSiter(a,i) i=i+1; if a[i] then return i,a[i] end end
local function BSipairs(t)
    return BSiter,t,-1
end

for i,v in BSipairs{[0]=0,1,2,3} do print(i,v) end

local dat_lut = {
    len = 4;
    mem = { };
}

for i = 0,3 do
    local nmat = { len = math.random(1,16),m={} }
    for i = 0,nmat.len-1 do nmat.m[i] = math.random(0,255) end
    dat_lut.mem[i] = nmat
end


local function arradd(t,v) t[#t+1] = v end
local function u8str(n) return string.char(n&0xFF) end
local function u16str(n) return u8str(n)..u8str(n>>8) end
local function u32str(n) return u16str(n)..u16str(n>>16) end

local function dat_save(dat)
    local ptrtab = {}
    local dattab = {ptrtab}
    -- save pointers
    local datlen = dat.len
    arradd(ptrtab,u16str(datlen))
    --> get size of pointer lut
    local ptrend = 2
    for i,d in pairs(dat.mem) do
        ptrend = ptrend + 4
    end
    --> size of each dat struct is 2+len
    local ptroff = 0
    for i,d in BSipairs(dat.mem) do
        print(("dat[i].len: %04X"):format(d.len))
        arradd(ptrtab,u32str(ptrend + ptroff))
        ptroff = ptroff + (2+d.len)
    end
    -- save data
    for i = 0,dat.len-1 do
        local d = dat.mem[i]
        arradd(dattab,u16str(d.len))
        for b=0,d.len-1 do arradd(dattab,u8str(d.m[b])) end
    end
    -- serialize
    dattab[1] = table.concat(ptrtab)
    local datstr = table.concat(dattab)
    return datstr
end

local str = dat_save(dat_lut)
local f = io.open("dat.bin",'wb')
f:write(str); f:close()