nNum 当前数字
n 保留小数点位数
function getPreciseDecimal(nNum, n)
if type(nNum) ~= "number" then
return nNum;
end
n = n or 0;
n = math.floor(n)
if n < 0 then
n = 0;
end
local nDecimal = 10 ^ n
local nTemp = math.floor(nNum * nDecimal);
local nRet = nTemp / nDecimal;
return nRet;
end