#-----------------------------------------------------------------------------
#
#  Bignum root
#
#  Returns null pointer if not perfect root.
#
#  The sign of the radicand is ignored.
#
#-----------------------------------------------------------------------------


mroot = (n, index) ->
  # this doesn't quite work
  #return n.pow(1/index +  0.0000000000000001)

  # sign of radicand ignored
  n = n.abs()

  i = 0
  j = 0
  k = 0

  if (index == 0)
    stop("root index is zero")

  # count number of bits
  k = 0
  while n.shiftRight(k) > 0
    k++
  
  if (k == 0)
    return mint(0)

  # initial guess

  k = Math.floor((k - 1) / index)

  j = Math.floor(k / 32 + 1)
  x = bigInt(j)

  for i in [0...j]
    # zero-out the ith bit
    x = x.and(bigInt(1).shiftLeft(i).not())

  while (k >= 0)
    # set the kth bit
    x = x.or(bigInt(1).shiftLeft(k))

    y = mpow(x, index)
    switch (mcmp(y, n))
      when 0
        return x
      when 1
        #mp_clr_bit(x, k)
        # clear the kth bit
        x = x.and(bigInt(1).shiftLeft(k).not())
    k--

  return 0


#if SELFTEST