md5 = {
    _VERSION = "md5.lua 0.5.0",
    _DESCRIPTION = "MD5 computation in Lua (5.1)",
    _URL = "https://github.com/kikito/md5.lua",
    _LICENSE = [[
    MIT LICENSE

    Copyright (c) 2013 Enrique García Cota + Adam Baldwin + hanzao + Equi 4 Software

    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the
    "Software"), to deal in the Software without restriction, including
    without limitation the rights to use, copy, modify, merge, publish,
    distribute, sublicense, and/or sell copies of the Software, and to
    permit persons to whom the Software is furnished to do so, subject to
    the following conditions:

    The above copyright notice and this permission notice shall be included
    in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
    OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
    IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
    CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
    TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
    SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  ]]
}

-- bit lib implementions

local floor, abs, max = math.floor, math.abs, math.max
local char, byte, format, rep, sub =
string.char, string.byte, string.format, string.rep, string.sub

local function check_int(n)
    -- checking not float
    if (n - floor(n) > 0) then
        error("trying to use bitwise operation on non-integer!")
    end
end

local function tbl2number(tbl)
    local n = #tbl

    local rslt = 0
    local power = 1
    for i = 1, n do
        rslt = rslt + tbl[i] * power
        power = power * 2
    end

    return rslt
end

local function expand(tbl_m, tbl_n)
    local big = {}
    local small = {}
    if (#tbl_m > #tbl_n) then
        big = tbl_m
        small = tbl_n
    else
        big = tbl_n
        small = tbl_m
    end
    -- expand small
    for i = #small + 1, #big do
        small[i] = 0
    end
end

local to_bits -- needs to be declared before bit_not

local function bit_not(n)
    local tbl = to_bits(n)
    local size = max(#tbl, 32)
    for i = 1, size do
        if (tbl[i] == 1) then
            tbl[i] = 0
        else
            tbl[i] = 1
        end
    end
    return tbl2number(tbl)
end

-- defined as local above
to_bits = function(n)
    check_int(n)
    if (n < 0) then
        -- negative
        return to_bits(bit_not(abs(n)) + 1)
    end
    -- to bits table
    local tbl = {}
    local cnt = 1
    while (n > 0) do
        local last = math.mod(n, 2)
        if (last == 1) then
            tbl[cnt] = 1
        else
            tbl[cnt] = 0
        end
        n = (n - last) / 2
        cnt = cnt + 1
    end

    return tbl
end

local function bit_or(m, n)
    local tbl_m = to_bits(m)
    local tbl_n = to_bits(n)
    expand(tbl_m, tbl_n)

    local tbl = {}
    local rslt = max(#tbl_m, #tbl_n)
    for i = 1, rslt do
        if (tbl_m[i] == 0 and tbl_n[i] == 0) then
            tbl[i] = 0
        else
            tbl[i] = 1
        end
    end

    return tbl2number(tbl)
end

local function bit_and(m, n)
    local tbl_m = to_bits(m)
    local tbl_n = to_bits(n)
    expand(tbl_m, tbl_n)

    local tbl = {}
    local rslt = max(#tbl_m, #tbl_n)
    for i = 1, rslt do
        if (tbl_m[i] == 0 or tbl_n[i] == 0) then
            tbl[i] = 0
        else
            tbl[i] = 1
        end
    end

    return tbl2number(tbl)
end

local function bit_xor(m, n)
    local tbl_m = to_bits(m)
    local tbl_n = to_bits(n)
    expand(tbl_m, tbl_n)

    local tbl = {}
    local rslt = max(#tbl_m, #tbl_n)
    for i = 1, rslt do
        if (tbl_m[i] ~= tbl_n[i]) then
            tbl[i] = 1
        else
            tbl[i] = 0
        end
    end

    return tbl2number(tbl)
end

local function bit_rshift(n, bits)
    check_int(n)

    local high_bit = 0
    if (n < 0) then
        -- negative
        n = bit_not(abs(n)) + 1
        high_bit = 2147483648 -- 0x80000000
    end

    for i = 1, bits do
        n = n / 2
        n = bit_or(floor(n), high_bit)
    end
    return floor(n)
end

local function bit_lshift(n, bits)
    check_int(n)

    if (n < 0) then
        -- negative
        n = bit_not(abs(n)) + 1
    end

    for i = 1, bits do
        n = n * 2
    end
    return bit_and(n, 4294967295) -- 0xFFFFFFFF
end

-- convert little-endian 32-bit int to a 4-char string
local function lei2str(i)
    local f = function(s) return char(bit_and(bit_rshift(i, s), 255)) end
    return f(0) .. f(8) .. f(16) .. f(24)
end

-- convert raw string to big-endian int
local function str2bei(s)
    local v = 0
    for i = 1, #s do
        v = v * 256 + byte(s, i)
    end
    return v
end

-- convert raw string to little-endian int
local function str2lei(s)
    local v = 0
    for i = #s, 1, -1 do
        v = v * 256 + byte(s, i)
    end
    return v
end

-- cut up a string in little-endian ints of given size
local function cut_le_str(s, ...)
    local o, r = 1, {}
    local args = { ... }
    for i = 1, #args do
        table.insert(r, str2lei(sub(s, o, o + args[i] - 1)))
        o = o + args[i]
    end
    return r
end

local swap = function(w) return str2bei(lei2str(w)) end

local function hex2binaryaux(hexval)
    return char(tonumber(hexval, 16))
end

local function hex2binary(hex)
    local result, _ = hex:gsub('..', hex2binaryaux)
    return result
end

-- An MD5 mplementation in Lua, requires bitlib (hacked to use LuaBit from above, ugh)
-- 10/02/2001 jcw@equi4.com

local FF = 0xffffffff
local CONSTS = {
    0xd76aa478, 0xe8c7b756, 0x242070db, 0xc1bdceee,
    0xf57c0faf, 0x4787c62a, 0xa8304613, 0xfd469501,
    0x698098d8, 0x8b44f7af, 0xffff5bb1, 0x895cd7be,
    0x6b901122, 0xfd987193, 0xa679438e, 0x49b40821,
    0xf61e2562, 0xc040b340, 0x265e5a51, 0xe9b6c7aa,
    0xd62f105d, 0x02441453, 0xd8a1e681, 0xe7d3fbc8,
    0x21e1cde6, 0xc33707d6, 0xf4d50d87, 0x455a14ed,
    0xa9e3e905, 0xfcefa3f8, 0x676f02d9, 0x8d2a4c8a,
    0xfffa3942, 0x8771f681, 0x6d9d6122, 0xfde5380c,
    0xa4beea44, 0x4bdecfa9, 0xf6bb4b60, 0xbebfbc70,
    0x289b7ec6, 0xeaa127fa, 0xd4ef3085, 0x04881d05,
    0xd9d4d039, 0xe6db99e5, 0x1fa27cf8, 0xc4ac5665,
    0xf4292244, 0x432aff97, 0xab9423a7, 0xfc93a039,
    0x655b59c3, 0x8f0ccc92, 0xffeff47d, 0x85845dd1,
    0x6fa87e4f, 0xfe2ce6e0, 0xa3014314, 0x4e0811a1,
    0xf7537e82, 0xbd3af235, 0x2ad7d2bb, 0xeb86d391,
    0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476
}

local f = function(x, y, z) return bit_or(bit_and(x, y), bit_and(-x - 1, z)) end
local g = function(x, y, z) return bit_or(bit_and(x, z), bit_and(y, -z - 1)) end
local h = function(x, y, z) return bit_xor(x, bit_xor(y, z)) end
local i = function(x, y, z) return bit_xor(y, bit_or(x, -z - 1)) end
local z = function(f, a, b, c, d, x, s, ac)
    a = bit_and(a + f(b, c, d) + x + ac, FF)
    -- be *very* careful that left shift does not cause rounding!
    return bit_or(bit_lshift(bit_and(a, bit_rshift(FF, s)), s), bit_rshift(a, 32 - s)) + b
end

local function transform(A, B, C, D, X)
    local a, b, c, d = A, B, C, D
    local t = CONSTS

    a = z(f, a, b, c, d, X[0], 7, t[1])
    d = z(f, d, a, b, c, X[1], 12, t[2])
    c = z(f, c, d, a, b, X[2], 17, t[3])
    b = z(f, b, c, d, a, X[3], 22, t[4])
    a = z(f, a, b, c, d, X[4], 7, t[5])
    d = z(f, d, a, b, c, X[5], 12, t[6])
    c = z(f, c, d, a, b, X[6], 17, t[7])
    b = z(f, b, c, d, a, X[7], 22, t[8])
    a = z(f, a, b, c, d, X[8], 7, t[9])
    d = z(f, d, a, b, c, X[9], 12, t[10])
    c = z(f, c, d, a, b, X[10], 17, t[11])
    b = z(f, b, c, d, a, X[11], 22, t[12])
    a = z(f, a, b, c, d, X[12], 7, t[13])
    d = z(f, d, a, b, c, X[13], 12, t[14])
    c = z(f, c, d, a, b, X[14], 17, t[15])
    b = z(f, b, c, d, a, X[15], 22, t[16])

    a = z(g, a, b, c, d, X[1], 5, t[17])
    d = z(g, d, a, b, c, X[6], 9, t[18])
    c = z(g, c, d, a, b, X[11], 14, t[19])
    b = z(g, b, c, d, a, X[0], 20, t[20])
    a = z(g, a, b, c, d, X[5], 5, t[21])
    d = z(g, d, a, b, c, X[10], 9, t[22])
    c = z(g, c, d, a, b, X[15], 14, t[23])
    b = z(g, b, c, d, a, X[4], 20, t[24])
    a = z(g, a, b, c, d, X[9], 5, t[25])
    d = z(g, d, a, b, c, X[14], 9, t[26])
    c = z(g, c, d, a, b, X[3], 14, t[27])
    b = z(g, b, c, d, a, X[8], 20, t[28])
    a = z(g, a, b, c, d, X[13], 5, t[29])
    d = z(g, d, a, b, c, X[2], 9, t[30])
    c = z(g, c, d, a, b, X[7], 14, t[31])
    b = z(g, b, c, d, a, X[12], 20, t[32])

    a = z(h, a, b, c, d, X[5], 4, t[33])
    d = z(h, d, a, b, c, X[8], 11, t[34])
    c = z(h, c, d, a, b, X[11], 16, t[35])
    b = z(h, b, c, d, a, X[14], 23, t[36])
    a = z(h, a, b, c, d, X[1], 4, t[37])
    d = z(h, d, a, b, c, X[4], 11, t[38])
    c = z(h, c, d, a, b, X[7], 16, t[39])
    b = z(h, b, c, d, a, X[10], 23, t[40])
    a = z(h, a, b, c, d, X[13], 4, t[41])
    d = z(h, d, a, b, c, X[0], 11, t[42])
    c = z(h, c, d, a, b, X[3], 16, t[43])
    b = z(h, b, c, d, a, X[6], 23, t[44])
    a = z(h, a, b, c, d, X[9], 4, t[45])
    d = z(h, d, a, b, c, X[12], 11, t[46])
    c = z(h, c, d, a, b, X[15], 16, t[47])
    b = z(h, b, c, d, a, X[2], 23, t[48])

    a = z(i, a, b, c, d, X[0], 6, t[49])
    d = z(i, d, a, b, c, X[7], 10, t[50])
    c = z(i, c, d, a, b, X[14], 15, t[51])
    b = z(i, b, c, d, a, X[5], 21, t[52])
    a = z(i, a, b, c, d, X[12], 6, t[53])
    d = z(i, d, a, b, c, X[3], 10, t[54])
    c = z(i, c, d, a, b, X[10], 15, t[55])
    b = z(i, b, c, d, a, X[1], 21, t[56])
    a = z(i, a, b, c, d, X[8], 6, t[57])
    d = z(i, d, a, b, c, X[15], 10, t[58])
    c = z(i, c, d, a, b, X[6], 15, t[59])
    b = z(i, b, c, d, a, X[13], 21, t[60])
    a = z(i, a, b, c, d, X[4], 6, t[61])
    d = z(i, d, a, b, c, X[11], 10, t[62])
    c = z(i, c, d, a, b, X[2], 15, t[63])
    b = z(i, b, c, d, a, X[9], 21, t[64])

    return A + a, B + b, C + c, D + d
end

----------------------------------------------------------------
function md5.sumhexa(s)
    local msgLen = #s
    local padLen = 56 - msgLen % 64

    if msgLen % 64 > 56 then padLen = padLen + 64 end

    if padLen == 0 then padLen = 64 end

    s = s .. char(128) .. rep(char(0), padLen - 1) .. lei2str(8 * msgLen) .. lei2str(0)

    assert(#s % 64 == 0)

    local t = CONSTS
    local a, b, c, d = t[65], t[66], t[67], t[68]

    for i = 1, #s, 64 do
        local X = cut_le_str(sub(s, i, i + 63), 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4)
        assert(#X == 16)
        X[0] = table.remove(X, 1) -- zero based!
        a, b, c, d = transform(a, b, c, d, X)
    end

    return format("%08x%08x%08x%08x", swap(a), swap(b), swap(c), swap(d))
end

function md5.sum(s)
    return hex2binary(md5.sumhexa(s))
end
