-- 初始化
  function math.randomInit(seed)
  	seed = seed or skynet.timex()
  	math.randomseed(tonumber(tostring(seed):reverse():sub(1,6)))
  end
  
  -- 随机浮点数
  function math.randomFloat(lower, greater)
      return math.min(lower, greater) + math.random()  * math.abs(greater - lower);
  end
  
  function math.randomInt(lower, greater)
  	return math.random(math.min(lower, greater), math.max(lower, greater))
  end
  
  -- 根据权重值从数据集合里面随机出
  -- @param dataset	数据集合
  -- @param field 	权重域
  function math.randWeight(dataset, field)
  	if not dataset then return nil end
  
  	field = field or "weight"
  
  	-- 计算权值总和
  	local weightSum = 0
  	for key, value in pairs(dataset) do
  		weightSum = weightSum + tonumber(value[field])
  	end
  
  	local randWeight = math.randomFloat(0, weightSum)
  	for key, value in pairs(dataset) do
  		if tonumber(value[field]) > 0 then
  			if randWeight > tonumber(value[field]) then
  				randWeight = randWeight - tonumber(value[field])
  			else
  				return key
  			end
  		end
  	end
  
  	return nil
  end