Java BigIntegerMath ceilingPowerOfTwo() 函数

Guava的BigIntegerMath类的 ceilingPowerOfTwo(BigInteger x) 方法返回大于或等于x的 最小 二 阶幂 。这相当于BigInteger.valueOf(2).pow(log2(x, CEILING) )。

语法

public static BigInteger 
    ceilingPowerOfTwo(BigInteger x)

参数。该方法以数字x为参数，要找到其上限为2的幂。

返回值。该方法返回给定数字x的2的最大功率。

异常： 如果x<=0，该方法会产生 IllegalArgumentException 。

下面的例子说明了BigIntegerMath. ceilingPowerOfTwo()方法。

例1 :

// Java code to show implementation of
// ceilingPowerOfTwo(BigInteger x) method
// of Guava's BigIntegerMath class
  
import java.math.*;
import com.google.common.math.BigIntegerMath;
  
class GFG {
  
    // Driver code
    public static void main(String args[])
    {
        BigInteger n1 = BigInteger.valueOf(25);
  
        // Using ceilingPowerOfTwo(BigInteger x) method of
        // Guava's BigIntegerMath class
        BigInteger ans = BigIntegerMath.ceilingPowerOfTwo(n1);
  
        System.out.println("Smallest power of 2 greater "
                           + "than or equal to "
                           + n1 + " is: " + ans);
  
        BigInteger n2 = BigInteger.valueOf(65);
  
        // Using ceilingPowerOfTwo(BigInteger x) method of
        // Guava's BigIntegerMath class
        BigInteger ans1 = BigIntegerMath.ceilingPowerOfTwo(n2);
  
        System.out.println("Smallest power of 2 greater "
                           + "than or equal to "
                           + n2 + " is: " + ans1);
    }
}

输出。

Smallest power of 2 greater than or equal to 25 is: 32
Smallest power of 2 greater than or equal to 65 is: 128

例2 :

// Java code to show implementation of
// ceilingPowerOfTwo(BigInteger x) method
// of Guava's BigIntegerMath class
  
import java.math.*;
import com.google.common.math.BigIntegerMath;
  
class GFG {
  
    // Driver code
    public static void main(String args[])
    {
  
        try {
  
            BigInteger n = BigInteger.valueOf(0);
  
            // Using ceilingPowerOfTwo(BigInteger x) method of
            // Guava's BigIntegerMath class
            // This should raise "IllegalArgumentException"
            // as n is <= 0
            BigInteger ans = BigIntegerMath.ceilingPowerOfTwo(n);
  
            System.out.println("Smallest power of 2 greater "
                               + "than or equal to n is : " + ans);
        }
        catch (Exception e) {
            System.out.println("Exception: " + e);
        }
    }
}

输出。

Exception: java.lang.IllegalArgumentException: x (0) must be > 0

参考资料: https://google.github.io/guava/releases/21.0/api/docs/com/google/common/math/BigIntegerMath.html#ceilingPowerOfTwo-java.math.BigInteger-