npm package: @stdlib/math-base-special-roundn
Description: Round a double-precision floating-point number to the nearest multiple of 10^n.
Author: The Stdlib Authors
Latest version: 0.2.3

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</details>

# roundn

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> Round a double-precision floating-point number to the nearest multiple of 10^n.

<section class="installation">

## Installation

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

</section>

<section class="usage">

## Usage

```javascript
var roundn = require( '@stdlib/math-base-special-roundn' );
```

#### roundn( x, n )

Rounds a double-precision floating-point number to the nearest multiple of `10^n`.

```javascript
// Round a value to 2 decimal places:
var v = roundn( 3.141592653589793, -2 );
// returns 3.14

// If n = 0, `roundn` behaves like `round`:
v = roundn( 3.141592653589793, 0 );
// returns 3.0

// Round a value to the nearest thousand:
v = roundn( 12368.0, 3 );
// returns 12000.0
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   When operating on [floating-point numbers][ieee754] in bases other than `2`, rounding to specified digits can be **inexact**. For example,

    ```javascript
    var x = 0.2 + 0.1;
    // returns 0.30000000000000004

    // Should round to 0.3...
    var v = roundn( x, -16 );
    // returns 0.3000000000000001
    ```

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

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

var opts = {
    'dtype': 'float64'
};
var x = uniform( 100, -50.0, 50.0, opts );
var n = discreteUniform( 100, -5, 0, opts );

logEachMap( 'x: %0.4f. Number of decimals: %d. Rounded: %0.4f.', x, n, roundn );
```

</section>

<!-- /.examples -->

<!-- C interface documentation. -->

* * *

<section class="c">

## C APIs

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<section class="intro">

</section>

<!-- /.intro -->

<!-- C usage documentation. -->

<section class="usage">

### Usage

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

#### stdlib_base_roundn( x, n )

Rounds a double-precision floating-point number to the nearest multiple of `10^n`.

```c
double y = stdlib_base_roundn( 3.14, -2 );
// returns 3.14
```

The function accepts the following arguments:

-   **x**: `[in] double` input value.
-   **n**: `[in] int32_t` integer power of 10.

```c
double stdlib_base_roundn( const double x, const int32_t n );
```

</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/roundn.h"
#include <stdio.h>

int main( void ) {
    const double x[] = { 3.14, -3.14, 0.0, 0.0/0.0 };

    double y;
    int i;
    for ( i = 0; i < 4; i++ ) {
        y = stdlib_base_roundn( x[ i ], -2 );
        printf( "roundn(%lf) = %lf\n", x[ i ], y );
    }
}
```

</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/ceiln`][@stdlib/math/base/special/ceiln]</span><span class="delimiter">: </span><span class="description">round a numeric value to the nearest multiple of 10^n toward positive infinity.</span>
-   <span class="package-name">[`@stdlib/math-base/special/floorn`][@stdlib/math/base/special/floorn]</span><span class="delimiter">: </span><span class="description">round a double-precision floating-point number to the nearest multiple of 10^n toward negative infinity.</span>
-   <span class="package-name">[`@stdlib/math-base/special/round`][@stdlib/math/base/special/round]</span><span class="delimiter">: </span><span class="description">round a numeric value to the nearest integer.</span>
-   <span class="package-name">[`@stdlib/math-base/special/roundb`][@stdlib/math/base/special/roundb]</span><span class="delimiter">: </span><span class="description">round a numeric value to the nearest multiple of b^n on a linear scale.</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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---

## License

See [LICENSE][stdlib-license].


## Copyright

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

</section>

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[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/math-base-special-roundn/main/LICENSE

[ieee754]: https://en.wikipedia.org/wiki/IEEE_754-1985

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

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

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

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

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