# BigIntegerMath log2() function | Guava | Java

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:

 `// 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)); ` `    ``} ` `} `

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

 `// 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); ` `        ``} ` `    ``} ` `} `

Output:

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

My Personal Notes arrow_drop_up Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.

Article Tags :
Practice Tags :

Be the First to upvote.

Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.