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# Binary Logarithm

> Evaluate the [binary logarithm][binary-logarithm].

<section class="intro">

The [binary logarithm][binary-logarithm] (logarithm with base 2) is defined for any positive real number as

<!-- <equation class="equation" label="eq:binary_logarithm" align="center" raw="\quad \log_{2} \left( x \right) = y \quad \text{such that} \quad 2^y = x" alt="Equation for the binary logarithm."> -->

<div class="equation" align="center" data-raw-text="\quad \log_{2} \left( x \right) = y \quad \text{such that} \quad 2^y = x" data-equation="eq:binary_logarithm">
    <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@8cb4d022f6163be6523964802725ed2a74f2497b/lib/node_modules/@stdlib/math/base/special/log2/docs/img/equation_binary_logarithm.svg" alt="Equation for the binary logarithm.">
    <br>
</div>

<!-- </equation> -->

</section>

<!-- /.intro -->

<section class="usage">

## 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
```

</section>

<!-- /.usage -->

<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```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 ) );
}
```

</section>

<!-- /.examples -->

<section class="links">

[binary-logarithm]: https://en.wikipedia.org/wiki/Binary_logarithm

</section>

<!-- /.links -->