npm package: @stdlib/math-base-special-log2
Description: Binary logarithm (base 2).
Author: The Stdlib Authors
Latest version: 0.3.1

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</details>

# Binary Logarithm

[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] <!-- [![dependencies][dependencies-image]][dependencies-url] -->

> 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="installation">

## Installation

```bash
npm install @stdlib/math-base-special-log2
```

</section>

<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 discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var logEachMap = require( '@stdlib/console-log-each-map' );
var log2 = require( '@stdlib/math-base-special-log2' );

var opts = {
    'dtype': 'float64'
};
var x = discreteUniform( 100, 0, 100, opts );

logEachMap( 'log2(%d) = %0.4f', x, log2 );
```

</section>

<!-- /.examples -->

<!-- C interface documentation. -->

* * *

<section class="c">

## C APIs

<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->

<section class="intro">

</section>

<!-- /.intro -->

<!-- C usage documentation. -->

<section class="usage">

### Usage

```c
#include "stdlib/math/base/special/log2.h"
```

#### stdlib_base_log2( x )

Evaluates the binary logarithm.

```c
double out = stdlib_base_log2( 4.0 );
// returns 2.0
```

The function accepts the following arguments:

-   **x**: `[in] double` input value.

```c
double stdlib_base_log2( const double x );
```

</section>

<!-- /.usage -->

<!-- C API usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

</section>

<!-- /.notes -->

<!-- C API usage examples. -->

<section class="examples">

### Examples

```c
#include "stdlib/math/base/special/log2.h"
#include <stdlib.h>
#include <stdio.h>

int main( void ) {
    double x;
    double v;
    int i;
    for ( i = 0; i < 100; i++ ) {
        x = ( ( (double)rand() / (double)RAND_MAX ) * 100.0 );
        v = stdlib_base_log2( x );
        printf( "log2(%lf) = %lf\n", x, v );
    }
}
```

</section>

<!-- /.examples -->

</section>

<!-- /.c -->

<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

<section class="related">

* * *

## See Also

-   <span class="package-name">[`@stdlib/math-base/special/exp2`][@stdlib/math/base/special/exp2]</span><span class="delimiter">: </span><span class="description">base 2 exponential function.</span>
-   <span class="package-name">[`@stdlib/math-base/special/ln`][@stdlib/math/base/special/ln]</span><span class="delimiter">: </span><span class="description">evaluate the natural logarithm of a double-precision floating-point number.</span>
-   <span class="package-name">[`@stdlib/math-base/special/log`][@stdlib/math/base/special/log]</span><span class="delimiter">: </span><span class="description">compute the base `b` logarithm of a double-precision floating-point number.</span>

</section>

<!-- /.related -->

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<section class="main-repo" >

* * *

## Notice

This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib].

#### Community

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---

## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

</section>

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[stdlib]: https://github.com/stdlib-js/stdlib

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[umd]: https://github.com/umdjs/umd
[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules

[deno-url]: https://github.com/stdlib-js/math-base-special-log2/tree/deno
[deno-readme]: https://github.com/stdlib-js/math-base-special-log2/blob/deno/README.md
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[branches-url]: https://github.com/stdlib-js/math-base-special-log2/blob/main/branches.md

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

<!-- <related-links> -->

[@stdlib/math/base/special/exp2]: https://www.npmjs.com/package/@stdlib/math-base-special-exp2

[@stdlib/math/base/special/ln]: https://www.npmjs.com/package/@stdlib/math-base-special-ln

[@stdlib/math/base/special/log]: https://www.npmjs.com/package/@stdlib/math-base-special-log

<!-- </related-links> -->

</section>

<!-- /.links -->