boidsutils.java

j2me小游戏 j2me小游戏 j2me小游戏 j2me小游戏

// Copyright 2002 Nokia Corporation. 
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package example.boids;

import java.util.Random;


class BoidsUtils
{
    private static Random random = new Random();


    private BoidsUtils()
    {
        // private so no-one can create an instance of this class
    }


    static int random(int scale)
    {
        int randomInt = random.nextInt();
        // extend to long, but remove sign-extend
        long randomIntAsLong = (long)randomInt & 0xFFFFFFFFL;
        int result = (int)((randomIntAsLong * (long)scale) >> 32);
        return result;
    }

    // This seems to produce the square root rounded down to the next
    // integer, except for numbers very near the next square, when we
    // get the square root rounded up to the next integer. That's good
    // enough for our purposes here anyway. In use in the boids MIDlet,
    // it averages about 14 iterations per use.
    static int squareRoot(int square)
    {
        int guess = square;
        if (square < 0)
        {
            throw new IllegalArgumentException(
                                         "Negative argument to squareRoot");
        }
        else if (square != 0)
        {
            int oldGuess;
            do
            {
                // Newton's method
                oldGuess = guess;
                guess = (oldGuess + square / oldGuess) >> 1;
            } while ((guess < oldGuess) && (guess > 0));
        }

        return guess;
    }
}