【高级技巧】布隆过滤器：兑换码核销的预判层

local bits = {}
local function setBit(pos)
    local cell = math.floor(pos / 32) + 1
    local off = 2 ^ (pos % 32)
    bits[cell] = (bits[cell] or 0) + off - (math.floor((bits[cell] or 0) / off) % 2) * off
end
local function getBit(pos)
    local cell = math.floor(pos / 32) + 1
    local off = 2 ^ (pos % 32)
    return math.floor((bits[cell] or 0) / off) % 2
end
local function hashN(s, n)
    local h = 0
    for i = 1, #s do
        h = (h * 31 + string.byte(s, i) * n) % 65536
    end
    return h
end
local function bloomAdd(code)
    for n = 1, 3 do
        setBit(hashN(code, n))
    end
end
local function bloomMayContain(code)
    for n = 1, 3 do
        if getBit(hashN(code, n)) == 0 then
            return false
        end
    end
    return true
end

local function redeem(actorName, code)
    local actor = getplayerbyname(actorName)
    if not bloomMayContain(code) then
        sendmsg(actor, 1, "兑换码无效。")
        return false
    end
    return checkRealTable(code)
end