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BigIntegerMath log2() function | Guava | Java
  • Last Updated : 15 Nov, 2018

The method log2(BigInteger x, RoundingMode mode) of Guava’s BigIntegerMath class returns the base-2 logarithm of x, rounded according to the specified rounding mode.

Syntax:

public static int log2(BigInteger x, RoundingMode mode)

Parameters: This method takes the following parameters:

  • x: The BigInteger number whose log is to be found.
  • mode: The rounding mode for calculating the log of 2.

Return Value: This method returns the base-2 logarithm of x, rounded according to the specified rounding mode.

Exceptions: This method throws the following exceptions:



  • IllegalArgumentException: if x <= 0.
  • ArithmeticException: if mode is RoundingMode.UNNECESSARY and x is not a power of 2.

Enum RoundingMode

Enum Constant Description
CEILING Rounding mode to round towards positive infinity.
DOWN Rounding mode to round towards zero.
FLOOR Rounding mode to round towards negative infinity.
HALF_DOWN Rounding mode to round towards “nearest neighbor” unless both neighbors are equidistant, in which case round down.
HALF_EVEN Rounding mode to round towards the “nearest neighbor” unless both neighbors are equidistant, in which case, round towards the even neighbor.
HALF_UP Rounding mode to round towards “nearest neighbor” unless both neighbors are equidistant, in which case round up.
UNNECESSARY Rounding mode to assert that the requested operation has an exact result, hence no rounding is necessary.
UP Rounding mode to round away from zero.

Below examples illustrates the BigIntegerMath.log2() method:

Example 1:

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// 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));
    }
}

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Output:

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

Example 2: To show IllegalArgumentException

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// 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);
        }
    }
}

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Output:

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

Reference: 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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