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

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# truncb

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> Round a numeric value to the nearest multiple of b^n toward zero.

<section class="installation">

## Installation

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

</section>

<section class="usage">

## Usage

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

#### truncb( x, n, b )

Rounds a `numeric` value to the nearest multiple of `b^n` toward zero.

```javascript
// Round a value to 4 decimal places:
var v = truncb( 3.141592653589793, -4, 10 );
// returns 3.1415

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

// Round a value to the nearest multiple of two toward zero:
v = truncb( 5.0, 1, 2 );
// returns 4.0
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

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

</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 truncb = require( '@stdlib/math-base-special-truncb' );

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 = truncb( x, n, b );
    console.log( 'x: %d. %d^%d: %d. Rounded: %d.', x, b, n, pow( b, n ), v );
}
```

</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/truncb.h"
```

#### stdlib_base_truncb( x, n, b )

Rounds a `numeric` value to the nearest multiple of `b^n` toward zero.

```c
double out = stdlib_base_truncb( 3.141592653589793, -4, 10 );
// returns 3.1415
```

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_truncb( 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/truncb.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_truncb( x[ i ], n[ i ], b[ i ] );
        printf( "truncb(%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/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>
-   <span class="package-name">[`@stdlib/math-base/special/trunc`][@stdlib/math/base/special/trunc]</span><span class="delimiter">: </span><span class="description">round a double-precision floating-point number toward zero.</span>
-   <span class="package-name">[`@stdlib/math-base/special/truncn`][@stdlib/math/base/special/truncn]</span><span class="delimiter">: </span><span class="description">round a numeric value to the nearest multiple of 10^n toward zero.</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].

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

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

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

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

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

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