# JavaScript - Binary logarithm using bitwise operators

## JavaScript Bit Manipulation: Exercise-8 with Solution

Write a JavaScript program to calculate the binary logarithm (log2n) using bitwise operators.

From handwiki.org -
Binary logarithm:
In mathematics, the binary logarithm (log2n) is the power to which the number 2 must be raised to obtain the value n. That is, for any real number x,

For example, the binary logarithm of 1 is 0, the binary logarithm of 2 is 1, the binary logarithm of 4 is 2, and the binary logarithm of 32 is 5.
The binary logarithm is the logarithm to the base 2 and is the inverse function of the power of two function. As well as log2, an alternative notation for the binary logarithm is lb (the notation preferred by ISO 31-11 and ISO 80000-2).

Test Data:
(1) -> 0
(2) -> 1
(4) -> 2
(32) -> 5

Sample Solution:

JavaScript Code:

``````// Define a function to calculate the logarithm base 2 of a number
const log_Two = (n) => {
// Check if the input is not a number
if (typeof n!= "number") {
return 'It must be number!' // Return an error message
}
let result = 0; // Initialize the result variable to 0
// Loop to find the logarithm base 2 of the number
while (n >> 1) {
n >>= 1; // Right shift the number by 1 bit
result++; // Increment the result counter
}
return result; // Return the logarithm base 2 of the number
}
console.log(log_Two(1)) // Test the function with the number 1
console.log(log_Two(2)) // Test the function with the number 2
console.log(log_Two(4)) // Test the function with the number 4
console.log(log_Two(32)) // Test the function with the number 32
```
```

Output:

```0
1
2
5
```

Flowchart:

Live Demo:

See the Pen javascript-bit-manipulation-exercise-8 by w3resource (@w3resource) on CodePen.

* To run the code mouse over on Result panel and click on 'RERUN' button.*

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