sqlite变长整数

varint.lua

function varint_decode(...)
    t = 0
    l = 0
    for _, i in ipairs{...} do
        t = t*128 + bit32.extract(i, 0, 7)
        l = l + 1
        if bit32.btest(i, 7) == false then
            break
        end
    end
    return t, l
end

function varint_encode(t)
    i = 0
    l = 1
    v = {}
    repeat
        table.insert(v, 1, bit32.extract(t, 0, 7))
        t = bit32.rshift(t, 7)
    until t == 0
    for _, s in pairs(v) do
        i = i*256 + s + 0x80
    end
    i = i - 0x80 -- clear last highest bit
    return i, l
end


assert(varint_decode(0x7f) == 0x7f, 1)
assert(varint_decode(0x81, 0x00) == 0x80, 1)
assert(varint_decode(0x81, 0x91, 0xd1, 0xac, 0x78) == 0x12345678, 4)
assert(varint_decode(0x81, 0x81, 0x81, 0x81, 0x01) == 0x10204081, 4)

assert(varint_encode(0x7f) == 0x7f, 1)
assert(varint_encode(0x80) == 0x8100, 2)
assert(varint_encode(0x12345678) == 0x8191d1ac78, 5)
assert(varint_encode(0x10204081) == 0x8181818101, 5)