npm package: @stdlib/math-base-special-roundb
Description: Round a numeric value to the nearest multiple of b^n on a linear scale.
Author: The Stdlib Authors
Latest version: 0.3.1

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</details>

# roundb

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

> Round a numeric value to the nearest multiple of b^n on a linear scale.

<section class="installation">

## Installation

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

</section>

<section class="usage">

## Usage

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

#### roundb( x, n, b )

Rounds a `numeric` value to the nearest multiple of `b^n` on a linear scale.

```javascript
// Round a value to 2 decimal places:
var v = roundb( 3.141592653589793, -2, 10 );
// returns 3.14

// If n = 0 or b = 1, `roundb` behaves like `round`:
v = roundb( 3.141592653589793, 0, 2 );
// returns 3.0

// Round a value to the nearest multiple of two:
v = roundb( 5.0, 1, 2 );
// returns 6.0
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   Due to rounding error in [floating-point numbers][ieee754], rounding may **not** be exact. For example,

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

    // Should round to 0.3...
    var v = roundb( x, -16, 10 );
    // returns 0.3000000000000001
    ```

</section>

<!-- /.notes -->

<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 pow = require( '@stdlib/math-base-special-pow' );
var roundb = require( '@stdlib/math-base-special-roundb' );

var x;
var n;
var b;
var v;
var i;

for ( i = 0; i < 100; i++ ) {
    x = (randu()*100.0) - 50.0;
    n = round( (randu()*10.0) - 5.0 );
    b = round( randu()*10.0 );
    v = roundb( x, n, b );
    console.log( 'x: %d. %d^%d: %d. Rounded: %d.', x, b, n, pow( b, n ), v );
}
```

</section>

<!-- /.examples -->

<!-- C usage documentation. -->

<section class="usage">

### Usage

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

#### stdlib_base_roundb( x, n, b )

Rounds a `numeric` value to the nearest multiple of `b^n` on a linear scale.

```c
double out = stdlib_base_roundb( 3.141592653589793, -2, 10 );
// returns 3.14
```

The function accepts the following arguments:

-   **x**: `[in] double` input value.
-   **n**: `[in] int32_t` power.
-   **b**: `[in] int32_t` base.

```c
double stdlib_base_roundb( const double x, const int32_t n, const int32_t b );
```

</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/roundb.h"
#include <stdio.h>
#include <stdint.h>

int main( void ) {
    const double x[] = { -5.0, -3.89, -2.78, -1.67, -0.56, 0.56, 1.67, 2.78, 3.89, 5.0 };
    const int32_t n[] = { -4, -3, -2, -1, 0, 1, 2, 3, 4, 5 };
    const int32_t b[] = { 20, 19, 18, 17, 16, 15, 14, 13, 12, 11 };

    double v;
    int i;
    for ( i = 0; i < 10; i++ ) {
        v = stdlib_base_roundb( x[ i ], n[ i ], b[ i ] );
        printf( "roundb(%lf, %d, %d) = %lf\n", x[ i ], n[ i ], b[ i ], 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/ceilb`][@stdlib/math/base/special/ceilb]</span><span class="delimiter">: </span><span class="description">round a numeric value to the nearest multiple of b^n toward positive infinity.</span>
-   <span class="package-name">[`@stdlib/math-base/special/floorb`][@stdlib/math/base/special/floorb]</span><span class="delimiter">: </span><span class="description">round a numeric value to the nearest multiple of b^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/roundn`][@stdlib/math/base/special/roundn]</span><span class="delimiter">: </span><span class="description">round a double-precision floating-point number to the nearest multiple of 10^n.</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

[![Chat][chat-image]][chat-url]

---

## License

See [LICENSE][stdlib-license].


## Copyright

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

</section>

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

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

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

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

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

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</section>

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