md5 = {}

local char, byte, format, rep, sub =
  string.char, string.byte, string.format, string.rep, string.sub
local bit_or, bit_and, bit_not, bit_xor, bit_rshift, bit_lshift

do
  bit_not = bit.bnot

  local tobit = function(n)
    return n <= 0x7fffffff and n or -(bit_not(n) + 1)
  end

  local normalize = function(f)
    return function(a,b) return tobit(f(tobit(a), tobit(b))) end
  end

  bit_or, bit_and, bit_xor = normalize(bit.bor), normalize(bit.band), normalize(bit.bxor)
  bit_rshift, bit_lshift = normalize(bit.rshift), normalize(bit.lshift)
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

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

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 (ff,a,b,c,d,x,s,ac)
  a=bit_and(a+ff(b,c,d)+x+ac,0xFFFFFFFF)
  -- be *very* careful that left shift does not cause rounding!
  return bit_or(bit_lshift(bit_and(a,bit_rshift(0xFFFFFFFF,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 bit_and(A+a,0xFFFFFFFF),bit_and(B+b,0xFFFFFFFF),
         bit_and(C+c,0xFFFFFFFF),bit_and(D+d,0xFFFFFFFF)
end

----------------------------------------------------------------

local function md5_update(self, s)
  self.pos = self.pos + #s
  s = self.buf .. s
  for ii = 1, #s - 63, 64 do
    local X = cut_le_str(sub(s,ii,ii+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!
    self.a,self.b,self.c,self.d = transform(self.a,self.b,self.c,self.d,X)
  end
  self.buf = sub(s, math.floor(#s/64)*64 + 1, #s)
  return self
end

local function md5_finish(self)
  local msgLen = self.pos
  local padLen = 56 - msgLen % 64

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

  if padLen == 0 then padLen = 64 end

  local s = char(128) .. rep(char(0),padLen-1) .. lei2str(bit_and(8*msgLen, 0xFFFFFFFF)) .. lei2str(math.floor(msgLen/0x20000000))
  md5_update(self, s)

  assert(self.pos % 64 == 0)
  return lei2str(self.a) .. lei2str(self.b) .. lei2str(self.c) .. lei2str(self.d)
end

----------------------------------------------------------------

function md5.new()
  return { a = CONSTS[65], b = CONSTS[66], c = CONSTS[67], d = CONSTS[68],
           pos = 0,
           buf = '',
           update = md5_update,
           finish = md5_finish }
end

function md5.tohex(s)
  return format("%08x%08x%08x%08x", str2bei(sub(s, 1, 4)), str2bei(sub(s, 5, 8)), str2bei(sub(s, 9, 12)), str2bei(sub(s, 13, 16)))
end

function md5.sum(s)
  return md5.new():update(s):finish()
end

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