bigentermath log2()函数|番石榴| Java
原文:https://www . geesforgeks . org/bigintermath-log 2-function-guava-Java/
番石榴的 BigIntegerMath 类的方法log2(bigintermate x，舍入模式)返回 x 的以 2 为底的对数，根据指定的舍入模式进行舍入。
语法:
public static int log2(BigInteger x, RoundingMode mode)
参数:该方法取以下参数:
- × 0 : a large integer whose log you want to find.
- Mode : The rounding mode for calculating the logarithm of 2.
返回值:该方法返回 x 的以 2 为底的对数，根据指定的舍入方式进行舍入。
异常:此方法抛出以下异常:
- IllegalArgumentException:if x<= 0 .
- Arithmetic exception: If the mode is circular mode. No need, x is not a power of 2.
枚举舍入模式
| 枚举常数 | 描述 | | 【天花板】 | 舍入模式向正无穷大舍入。 | | DOWN | 舍入模式为向零舍入。 | | FLOOR | 舍入模式为向负无穷大舍入。 | | HALF _ DOWN | 舍入模式为向“最近邻居”舍入，除非两个邻居等距，在这种情况下舍入为 DOWN。 | | HALF _ EVEN | 舍入模式为向“最近邻居”舍入，除非两个邻居等距，在这种情况下，向偶数邻居舍入。 | | 【HALF _ UP】 | 取整模式为向“最近邻居”取整，除非两个邻居等距，在这种情况下取整。 | | 【不必要的】 | 舍入模式断言请求的操作有确切的结果，因此没有舍入的必要。 | | UP | 取整模式为远离零取整。 |
以下示例说明了 BigIntegerMath.log2()方法:
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));
}
}
输出:
Log base 2 of 1024 with rounding mode HALF_EVEN = 10
Log base 2 of 15 with rounding mode HALF_DOWN = 1
示例 2: 显示非法文档异常
// 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);
}
}
}
输出:
Exception: java.lang.IllegalArgumentException: x (-5) must be > 0
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