bint-mul.nim

proc `*%` *(x, y: BigInt): BigInt = 
  ## Multiply two BigInts treating them as positive.
  ## The result is aways a positive BigNum.  
  # TODO: avoid seq initialization by doing the first multiplication round
  # separatedly before.
  declareSL(x, y, shorter, longer, tmp)
  result = newBigInt(longer.len + shorter.len - 1)
  
  for i, a in shorter:
    result[i + longer.len - 1] = tmp.carry
    for j, b in longer:
      tmp = a * b + tmp.carry + result[i+j]
      result[i+j] = tmp.value
        
  if tmp.carry != 0:
    result.add(tmp.carry)