LUA implementation of PICO-8's fset()/fget() functions for use with TIC-80 (maybe)

fget.lua

local sprf={}

function fget(s,i)
  if sprf[s+1]==nil then sprf[s+1]=0 end
  if i==nil then
    return math.floor(sprf[s+1])
  else
    local b=2^i
    return sprf[s+1] % (2*b) >= b 
  end
end

function fset(s,i,b)
    if b==nil then
      sprf[s+1]=i
    else
      local e
      if sprf[s+1]==nil then
        sprf[s+1]=0
        e=false
      else
        e=fget(s,i)
      end
      if (e and not b) or (not e and b) then 
        sprf[s+1]=sprf[s+1]+(b and 2^i or -2^i)
      end
    end
end