java - Android 基础数学不及格

Question

这个问题已经有答案了:

已关闭 11 年前。

Possible Duplicate:
Java float division precision

我正在尝试修复我的一款游戏中的错误，并且需要计算最佳的图 block 大小。为此，我获取设备的屏幕分辨率、该级别的行数和列数，然后计算允许我的游戏使用最大屏幕空间的图 block 大小。然而，Android 似乎在基础数学方面表现不佳，在简单的除法运算上失去了精度。这是适当的代码:

while(!foundIt)
    {
        int tileArea = boxes*i*i; //Boxes = 20*26
        float ratio = displayArea/tileArea;  //displayArea = width*height
        Log.d("Balance", displayArea + "/" + tileArea);
        Log.d("Balance", boxes + ", " + i);
        Log.d("Balance", "Ratio: " + ratio);
        int last = 0;
        if(ratio>1)
        {
            if(last==LAST_WAS_LESS_THAN_ONE)
            {
                i--;
                foundIt=true;
            }
            last = LAST_WAS_MORE_THAN_ONE;
        }
        else if(ratio==1)
        {
            Log.d("Balance", "Found a perfect fit!!");
            foundIt=true;
        }
        else if(ratio<1)
        {
            if(last==LAST_WAS_MORE_THAN_ONE)
            {
                i--;
                foundIt=true;
            }
            last = LAST_WAS_LESS_THAN_ONE;
        }
        if(!foundIt)
        {
            i++;
        }
    }

以下是在 Nexus S 上运行的示例(分辨率:480 x 800):

06-18 13:20:45.808: D/Balance(1069): Width: 480 Height: 800
06-18 13:20:45.808: D/Balance(1069): 384000/520
06-18 13:20:45.808: D/Balance(1069): 520, 1
06-18 13:20:45.808: D/Balance(1069): Ratio: 738.0
06-18 13:20:45.808: D/Balance(1069): 384000/2080
06-18 13:20:45.808: D/Balance(1069): 520, 2
06-18 13:20:45.808: D/Balance(1069): Ratio: 184.0
06-18 13:20:45.808: D/Balance(1069): 384000/4680
06-18 13:20:45.808: D/Balance(1069): 520, 3
06-18 13:20:45.808: D/Balance(1069): Ratio: 82.0
06-18 13:20:45.808: D/Balance(1069): 384000/8320
06-18 13:20:45.808: D/Balance(1069): 520, 4
06-18 13:20:45.808: D/Balance(1069): Ratio: 46.0
06-18 13:20:45.808: D/Balance(1069): 384000/13000
06-18 13:20:45.808: D/Balance(1069): 520, 5
06-18 13:20:45.808: D/Balance(1069): Ratio: 29.0
06-18 13:20:45.808: D/Balance(1069): 384000/18720
06-18 13:20:45.808: D/Balance(1069): 520, 6
06-18 13:20:45.808: D/Balance(1069): Ratio: 20.0
06-18 13:20:45.808: D/Balance(1069): 384000/25480
06-18 13:20:45.808: D/Balance(1069): 520, 7
06-18 13:20:45.808: D/Balance(1069): Ratio: 15.0
06-18 13:20:45.808: D/Balance(1069): 384000/33280
06-18 13:20:45.808: D/Balance(1069): 520, 8
06-18 13:20:45.808: D/Balance(1069): Ratio: 11.0
06-18 13:20:45.808: D/Balance(1069): 384000/42120
06-18 13:20:45.808: D/Balance(1069): 520, 9
06-18 13:20:45.808: D/Balance(1069): Ratio: 9.0
06-18 13:20:45.808: D/Balance(1069): 384000/52000
06-18 13:20:45.808: D/Balance(1069): 520, 10
06-18 13:20:45.808: D/Balance(1069): Ratio: 7.0
06-18 13:20:45.808: D/Balance(1069): 384000/62920
06-18 13:20:45.808: D/Balance(1069): 520, 11
06-18 13:20:45.808: D/Balance(1069): Ratio: 6.0
06-18 13:20:45.808: D/Balance(1069): 384000/74880
06-18 13:20:45.808: D/Balance(1069): 520, 12
06-18 13:20:45.808: D/Balance(1069): Ratio: 5.0
06-18 13:20:45.808: D/Balance(1069): 384000/87880
06-18 13:20:45.808: D/Balance(1069): 520, 13
06-18 13:20:45.808: D/Balance(1069): Ratio: 4.0
06-18 13:20:45.808: D/Balance(1069): 384000/101920
06-18 13:20:45.808: D/Balance(1069): 520, 14
06-18 13:20:45.808: D/Balance(1069): Ratio: 3.0
06-18 13:20:45.808: D/Balance(1069): 384000/117000
06-18 13:20:45.808: D/Balance(1069): 520, 15
06-18 13:20:45.808: D/Balance(1069): Ratio: 3.0
06-18 13:20:45.808: D/Balance(1069): 384000/133120
06-18 13:20:45.812: D/Balance(1069): 520, 16
06-18 13:20:45.812: D/Balance(1069): Ratio: 2.0
06-18 13:20:45.816: D/Balance(1069): 384000/150280
06-18 13:20:45.816: D/Balance(1069): 520, 17
06-18 13:20:45.816: D/Balance(1069): Ratio: 2.0
06-18 13:20:45.816: D/Balance(1069): 384000/168480
06-18 13:20:45.816: D/Balance(1069): 520, 18
06-18 13:20:45.816: D/Balance(1069): Ratio: 2.0
06-18 13:20:45.816: D/Balance(1069): 384000/187720
06-18 13:20:45.816: D/Balance(1069): 520, 19
06-18 13:20:45.816: D/Balance(1069): Ratio: 2.0
06-18 13:20:45.816: D/Balance(1069): 384000/208000
06-18 13:20:45.816: D/Balance(1069): 520, 20
06-18 13:20:45.816: D/Balance(1069): Ratio: 1.0
06-18 13:20:45.816: D/Balance(1069): Found a perfect fit!!

在计算器上计算比率会导致精度损失。有人知道这是为什么吗？我的实现有问题吗？

Answer 1

从打印输出来看，displayArea和tileArea似乎被声明为int或long。在将结果提升为 float 类型并分配给 ratio 之前，您正在执行整数除法 (displayArea/tileArea) >.

既然要比较一个是否比另一个大，为什么不直接比较 displayArea 和 tileArea 呢？这比玩弄浮点运算要好得多。