math - 在 Blackberry 4.2 JDE 上调用 atan 函数

Question

我需要从我的 Blackberry Java 应用程序计算反正切值。不幸的是，黑莓 4.2 api 没有 Math.atan() 函数。 Blackberry JDE 的 4.6 版有它，但 4.2 版没有。

有人知道计算 atan 的解决方法吗？

Answer 1

来自 Arctan in J2ME by Stephen Zimmerman :

// calculation functions
public class Calculation {

    // Because J2ME has no floating point numbers,
    // some sort of fixed point math is required.
    // My implementation is simply to shift 10 places.
    // for example, 1024 (>> 10) = 1
    // and 512 (>> 10) = 0.5


public static final int[] AtanTable = { 0, 1, 2, 3, 5, 6, 7, 8, 10, 11, 12,
            13, 14, 16, 17, 18, 19, 20, 21, 22, 23, 25, 26, 27, 28, 29, 
            30, 30,31, 32, 33, 34, 35, 36, 37, 37, 38, 39, 40, 40, 41, 
            42, 43, 43, 44, 45 };

    // / returns angle 0->359 in degrees
    public static int atan(int Y, int X) {
        boolean swap = false;

        int top = Math.abs(Y);
        int bottom = Math.abs(X);
        if (top > bottom) {
            int btemp = bottom;
            bottom = top;
            top = btemp;
            swap = true;
        } else if (bottom == 0)
            return -300;

        // this should keep index inbounds [0, 45]
        int index = (top * 45) / bottom;
        int angle = AtanTable[index];

        if (swap)
            angle = 90 - angle;

        // X & Y += 180
        // X & !Y = ...90
        // !X & Y = ... 270
        if ((X < 0) && (Y < 0))
            angle += 180;
        else if (Y < 0) {
            angle = 90 - angle;
            angle += 270;
        } else if (X < 0) {
            angle = 90 - angle;
            angle += 90;
        }

        if (angle == 360)
            angle = 0;

        return angle;
    }
}