npm package: @stdlib/number-float64-base-ulp-difference
Description: Compute the number of representable double-precision floating-point values that separate two double-precision floating-point numbers along the real number line.
Author: The Stdlib Authors
Latest version: 0.1.1

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# ulpdiff

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> Compute the number of representable [double-precision][double-precision] floating-point values that separate two [double-precision][double-precision] floating-point numbers along the real number line.

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<section class="intro">

</section>

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<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/number-float64-base-ulp-difference
```

</section>

<section class="usage">

## Usage

```javascript
var ulpdiff = require( '@stdlib/number-float64-base-ulp-difference' );
```

#### ulpdiff( x, y )

Computes the number of representable [double-precision][double-precision] floating-point values that separate two [double-precision][double-precision] floating-point numbers along the real number line.

```javascript
var EPS = require( '@stdlib/constants-float64-eps' );

var d = ulpdiff( 1.0, 1.0+EPS );
// returns 1.0

d = ulpdiff( 1.0+EPS, 1.0 );
// returns 1.0

d = ulpdiff( 1.0, 1.0+EPS+EPS );
// returns 2.0

d = ulpdiff( 1.0, NaN );
// returns NaN

d = ulpdiff( NaN, 1.0 );
// returns NaN

d = ulpdiff( NaN, NaN );
// returns NaN
```

</section>

<!-- /.usage -->

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

<section class="notes">

## Notes

-   Adjacent [double-precision][double-precision] floating-point numbers differ by `1` [ulp][ulp] (unit in the last place).
-   Signed zeros differ only in the sign bit but are considered numerically equal, and thus their ULP difference is `0`.

</section>

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<section class="examples">

## Examples

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

```javascript
var EPS = require( '@stdlib/constants-float64-eps' );
var SMALLEST_SUBNORMAL = require( '@stdlib/constants-float64-smallest-subnormal' );
var ulpdiff = require( '@stdlib/number-float64-base-ulp-difference' );

var d = ulpdiff( 1.0, 1.0+EPS );
console.log( d );
// => 1.0

d = ulpdiff( 5.8364e-319, 5.8367e-319 );
console.log( d );
// => 6.0

d = ulpdiff( 0.0, SMALLEST_SUBNORMAL );
console.log( d );
// => 1.0

d = ulpdiff( 0.0, -0.0 );
console.log( d );
// => 0.0

d = ulpdiff( SMALLEST_SUBNORMAL, -SMALLEST_SUBNORMAL );
console.log( d );
// => 2.0
```

</section>

<!-- /.examples -->

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* * *

## 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].

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

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[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/number-float64-base-ulp-difference/main/LICENSE

[double-precision]: https://en.wikipedia.org/wiki/Double-precision_floating-point_format

[ulp]: https://en.wikipedia.org/wiki/Unit_in_the_last_place

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