# Binary Logarithm
> Evaluate the [binary logarithm][binary-logarithm].
The [binary logarithm][binary-logarithm] (logarithm with base 2) is defined for any positive real number as
## Usage
```javascript
var log2 = require( '@stdlib/math/base/special/log2' );
```
#### log2( x )
Evaluates the [binary logarithm][binary-logarithm].
```javascript
var v = log2( 4.0 );
// returns 2.0
v = log2( 0.0 );
// returns -Infinity
v = log2( Infinity );
// returns Infinity
v = log2( NaN );
// returns NaN
```
For negative numbers, the [binary logarithm][binary-logarithm] is **not** defined.
```javascript
var v = log2( -4.0 );
// returns NaN
```
## Examples
```javascript
var randu = require( '@stdlib/random/base/randu' );
var round = require( '@stdlib/math/base/special/round' );
var log2 = require( '@stdlib/math/base/special/log2' );
var x;
var i;
for ( i = 0; i < 100; i++ ) {
x = round( randu() * 100.0 );
console.log( 'log2(%d) = %d', x, log2( x ) );
}
```
[binary-logarithm]: https://en.wikipedia.org/wiki/Binary_logarithm
