Java Guava BigIntegerMath log2()用法及代碼示例

Guava BigIntegerMath類的方法log2(BigInteger x，RoundingMode模式)返回x的以2為底的對數，並根據指定的舍入模式進行四舍五入。

用法:

public static int log2(BigInteger x, RoundingMode mode)

參數：此方法采用以下參數：

x：要查找其日誌的BigInteger號。
mode：用於計算2的對數的舍入模式。

返回值：此方法返回x的以2為底的對數，並根據指定的舍入模式進行舍入。

異常：此方法引發以下異常：

IllegalArgumentException：如果x <= 0。
ArithmeticException：如果mode為RoundingMode.UNNECESSARY且x不是2的冪。

Enum RoundingMode

枚舉常量	描述
CEILING	舍入模式向正無窮大舍入。
DOWN	舍入模式向零舍入。
FLOOR	舍入模式向負無窮大舍入。
HALF_DOWN	除非兩個鄰居等距，否則舍入模式將朝“nearest neighbor”舍入。
HALF_EVEN	舍入模式向“nearest neighbor”舍入，除非兩個鄰居都等距，在這種情況下，向偶數鄰居舍入。
HALF_UP	除非兩個鄰居等距，否則舍入模式將朝“nearest neighbor”舍入。
UNNECESSARY	舍入模式可以斷言所請求的操作具有準確的結果，因此不需要舍入。
UP	舍入模式從零舍入。

以下示例說明了BigIntegerMath.log2()方法：

範例1：

// Java code to show implementation of 
// log2(BigInteger x, RoundingMode mode) 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 a1 = BigInteger.valueOf(1024); 
  
        // Using log2(BigInteger x, RoundingMode mode) 
        // method of Guava's BigIntegerMath class 
        // The RoundingMode HALF_EVEN rounds towards 
        // the "nearest neighbor" unless both neighbors 
        // are equidistant, in which case, round towards 
        // the even neighbor. 
        System.out.println("Log base 2 of " + a1 
                           + " with rounding mode HALF_EVEN = "
                           + BigIntegerMath 
                                 .log2(a1, 
                                        RoundingMode.HALF_EVEN)); 
  
        BigInteger a2 = BigInteger.valueOf(15); 
  
        // Using log2(BigInteger x, RoundingMode mode) 
        // method of Guava's BigIntegerMath class 
        // The RoundingMode HALF_DOWN rounds towards 
        // "nearest neighbor" unless both neighbors 
        // are equidistant, in which case round down. 
        System.out.println("Log base 2 of " + a2 
                           + " with rounding mode HALF_DOWN = "
                           + BigIntegerMath 
                                 .log10(a2, 
                                        RoundingMode.HALF_DOWN)); 
    } 
}

輸出：

Log base 2 of 1024 with rounding mode HALF_EVEN = 10
Log base 2 of 15 with rounding mode HALF_DOWN = 1

範例2：顯示IllegalArgumentException

// Java code to show implementation of 
// log2(BigInteger x, RoundingMode mode) 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 a1 = BigInteger.valueOf(-5); 
  
            // Using log2(BigInteger x, RoundingMode mode) 
            // method of Guava's BigIntegerMath class 
            // The RoundingMode HALF_EVEN rounds towards 
            // the "nearest neighbor" unless both neighbors 
            // are equidistant, in which case, round towards 
            // the even neighbor. 
            // This should throw "IllegalArgumentException" 
            // as a1 <= 0 
            System.out.println("Log base 2 of " + a1 
                               + " with rounding mode HALF_EVEN = "
                               + BigIntegerMath 
                                     .log2(a1, 
                                            RoundingMode.HALF_EVEN)); 
        } 
  
        catch (Exception e) { 
            System.out.println("Exception:" + e); 
        } 
    } 
}

輸出：

Exception:java.lang.IllegalArgumentException:x (-5) must be > 0

參考： https://google.github.io/guava/releases/21.0/api/docs/com/google/common/math/BigIntegerMath.html#log2-java.math.BigInteger-java.math.RoundingMode-

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