Java Guava | log2(int x, RoundingMode mode) method of IntMath

• Last Updated : 23 Jan, 2019

The log2(int x, RoundingMode mode) method of Guava’s IntMath 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(int x, RoundingMode mode)
```

Parameters : The method takes 2 parameters, where x is an integer 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 :

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

Enum RoundingMode

Enum ConstantDescription
CEILINGRounding mode to round towards positive infinity.
DOWNRounding mode to round towards zero.
FLOORRounding mode to round towards negative infinity.
HALF_DOWNRounding mode to round towards “nearest neighbor” unless both neighbors are equidistant, in which case round down.
HALF_EVENRounding mode to round towards the “nearest neighbor” unless both neighbors are equidistant, in which case, round towards the even neighbor.
HALF_UPRounding mode to round towards “nearest neighbor” unless both neighbors are equidistant, in which case round up.
UNNECESSARYRounding mode to assert that the requested operation has an exact result, hence no rounding is necessary.
UPRounding mode to round away from zero.

Below examples illustrate the implementation of log2() method of Guava IntMath:

Example 1 :

 `// Java code to show implementation of``// log2(int x, RoundingMode mode) method``// of Guava's IntMath class``import` `java.math.RoundingMode;``import` `com.google.common.math.IntMath;`` ` `class` `GFG {`` ` `    ``// Driver code``    ``public` `static` `void` `main(String args[])``    ``{``        ``int` `a1 = ``1542``;`` ` `        ``// Using log2(int x, RoundingMode mode)``        ``// method of Guava's IntMath 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(IntMath.log2(a1, RoundingMode.HALF_EVEN));`` ` `        ``int` `a2 = ``451``;`` ` `        ``// Using log2(int x, RoundingMode mode)``        ``// method of Guava's IntMath class``        ``// The RoundingMode HALF_DOWN rounds towards``        ``// "nearest neighbor" unless both neighbors``        ``// are equidistant, in which case round down.``        ``System.out.println(IntMath.log2(a2, RoundingMode.HALF_DOWN));``    ``}``}`

Output:

```11
9
```

Example 2 :

 `// Java code to show implementation of``// log2(int x, RoundingMode mode) method``// of Guava's IntMath class``import` `java.math.RoundingMode;``import` `com.google.common.math.IntMath;`` ` `class` `GFG {`` ` `    ``static` `int` `findlog2(``int` `x, RoundingMode mode)``    ``{``        ``try` `{``            ``// Using log2(int x, RoundingMode mode)``            ``// method of Guava's IntMath 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``            ``int` `ans = IntMath.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[])``    ``{``        ``int` `x = -``152``;`` ` `        ``try` `{`` ` `            ``// Function calling``            ``findlog2(x, RoundingMode.HALF_EVEN);``        ``}``        ``catch` `(Exception e) {``            ``System.out.println(e);``        ``}``    ``}``}`

Output:

```java.lang.IllegalArgumentException: x (-152) must be > 0
```

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