【入门夯实】数据校验位：关键存档的完整性校验

local function loadSignup(text)
    local name, seq = string.match(text, "([^,]+),(%d+)")
    return name, tonumber(seq)
end

local function checksum(text)
    local sum = 0
    for i = 1, #text do
        sum = sum + string.byte(text, i)
    end
    return sum % 65536
end
local function saveSignup(name, seq)
    local body = name .. "," .. seq
    return body .. "|" .. checksum(body)
end
local function loadSignup(text)
    local body, stored = string.match(text, "^(.+)|(%d+)$")
    if body == nil then
        return nil, "格式损坏"
    end
    if checksum(body) ~= tonumber(stored) then
        return nil, "校验不符，数据可能被截断"
    end
    local name, seq = string.match(body, "([^,]+),(%d+)")
    return name, tonumber(seq)
end

local name, seq, why = loadSignup(saved)
if name == nil then
    sendmsg(nil, 1, "报名档加载失败：" .. why)
end

local function checksumW(text)
    local sum = 0
    for i = 1, #text do
        sum = sum + string.byte(text, i) * (i % 7 + 1)
    end
    return sum % 65536
end