Java Guava | log2(long x, RoundingMode mode) of LongMath Class with Examples

Last Updated : 11 Jul, 2025
The method log2(long x, RoundingMode mode) of Guava's LongMath Class accepts two parameters and calculates the base-2 logarithmic value of the first parameter rounded according to the rounding mode specified by the second parameter. Syntax: 
public static int log2(long x, RoundingMode mode)
Parameters: The method takes 2 parameters, where x is a long and mode is a specified rounding mode. Return Value: This method returns Base-2 logarithm of x, rounded according to the specified rounding mode. Exceptions: This method throws following parameters:
  • IllegalArgumentException: if x <= 0.
  • ArithmeticException: if mode is RoundingMode.UNNECESSARY and x is not a power of two.

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 illustrate the implementation of log2() method of Guava LongMath: Example 1 : Java 
// Java code to show implementation of
// log2(long x, RoundingMode mode) method
// of Guava's LongMath class

import java.math.RoundingMode;
import com.google.common.math.LongMath;

class GFG {

    // Driver code
    public static void main(String args[])
    {
        long n1 = 1111;

        // Using log2(long x, RoundingMode mode)
        // method of Guava's LongMath 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(LongMath.log2(
            n1,
            RoundingMode.HALF_EVEN));

        long n2 = 205;

        // Using log2(long x, RoundingMode mode)
        // method of Guava's LongMath class
        // The RoundingMode HALF_DOWN rounds towards
        // "nearest neighbor" unless both neighbors
        // are equidistant, in which case round down.
        System.out.println(LongMath.log2(
            n2,
            RoundingMode.HALF_DOWN));
    }
}
Output: 
10
8
Example 2: Java 
// Java code to show implementation of
// log2(long x, RoundingMode mode) method
// of Guava's LongMath class

import java.math.RoundingMode;
import com.google.common.math.LongMath;

class GFG {

    static long findlog2(long x, RoundingMode mode)
    {
        try {
            // Using log2(long x, RoundingMode mode)
            // method of Guava's LongMath 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 x <= 0
            long ans = LongMath.log2(x, mode);

            // Return the answer
            return ans;
        }
        catch (Exception e) {
            System.out.println(e);
            return -1;
        }
    }

    // Driver code
    public static void main(String args[])
    {
        long x = -122;

        try {

            // Function calling
            findlog2(x, RoundingMode.HALF_EVEN);
        }
        catch (Exception e) {
            System.out.println(e);
        }
    }
}
Output: 
java.lang.IllegalArgumentException: x (-122) must be > 0
Reference: https://guava.dev/releases/20.0/api/docs/com/google/common/math/LongMath.html#log2-long-java.math.RoundingMode-
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