Compute the number of representable double-precision floating-point values that separate two double-precision floating-point numbers along the real number line.
npm install @stdlib/number-float64-base-ulp-differenceWe believe in a future in which the web is a preferred environment for numerical computation. To help realize this future, we've built stdlib. stdlib is a standard library, with an emphasis on numerical and scientific computation, written in JavaScript (and C) for execution in browsers and in Node.js. The library is fully decomposable, being architected in such a way that you can swap out and mix and match APIs and functionality to cater to your exact preferences and use cases. When you use stdlib, you can be absolutely certain that you are using the most thorough, rigorous, well-written, studied, documented, tested, measured, and high-quality code out there. To join us in bringing numerical computing to the web, get started by checking us out on GitHub, and please consider financially supporting stdlib. We greatly appreciate your continued support!
About stdlib...
[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url]
> 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.
``bash`
npm install @stdlib/number-float64-base-ulp-difference
`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
`
- Adjacent [double-precision][double-precision] floating-point numbers differ by 1 [ulp][ulp] (unit in the last place).0
- Signed zeros differ only in the sign bit but are considered numerically equal, and thus their ULP difference is .
`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
`
*
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]
---
See [LICENSE][stdlib-license].
Copyright © 2016-2026. The Stdlib [Authors][stdlib-authors].
[npm-image]: http://img.shields.io/npm/v/@stdlib/number-float64-base-ulp-difference.svg
[npm-url]: https://npmjs.org/package/@stdlib/number-float64-base-ulp-difference
[test-image]: https://github.com/stdlib-js/number-float64-base-ulp-difference/actions/workflows/test.yml/badge.svg?branch=v0.1.1
[test-url]: https://github.com/stdlib-js/number-float64-base-ulp-difference/actions/workflows/test.yml?query=branch:v0.1.1
[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/number-float64-base-ulp-difference/main.svg
[coverage-url]: https://codecov.io/github/stdlib-js/number-float64-base-ulp-difference?branch=main
[chat-image]: https://img.shields.io/badge/zulip-join_chat-brightgreen.svg
[chat-url]: https://stdlib.zulipchat.com
[stdlib]: https://github.com/stdlib-js/stdlib
[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors
[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/number-float64-base-ulp-difference/tree/deno
[deno-readme]: https://github.com/stdlib-js/number-float64-base-ulp-difference/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/number-float64-base-ulp-difference/tree/umd
[umd-readme]: https://github.com/stdlib-js/number-float64-base-ulp-difference/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/number-float64-base-ulp-difference/tree/esm
[esm-readme]: https://github.com/stdlib-js/number-float64-base-ulp-difference/blob/esm/README.md
[branches-url]: https://github.com/stdlib-js/number-float64-base-ulp-difference/blob/main/branches.md
[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