https://github.com/stdlib-js/number-float64-base-from-int64-bytes
Convert a signed 64-bit integer byte array to a double-precision floating-point number.
https://github.com/stdlib-js/number-float64-base-from-int64-bytes
base cast convert dbl double float64 int int64 integer javascript node node-js nodejs stdlib type types util utilities utility utils
Last synced: 10 months ago
JSON representation
Convert a signed 64-bit integer byte array to a double-precision floating-point number.
- Host: GitHub
- URL: https://github.com/stdlib-js/number-float64-base-from-int64-bytes
- Owner: stdlib-js
- License: apache-2.0
- Created: 2021-06-15T18:48:23.000Z (over 4 years ago)
- Default Branch: main
- Last Pushed: 2025-03-24T01:33:31.000Z (11 months ago)
- Last Synced: 2025-03-27T01:46:41.302Z (10 months ago)
- Topics: base, cast, convert, dbl, double, float64, int, int64, integer, javascript, node, node-js, nodejs, stdlib, type, types, util, utilities, utility, utils
- Language: JavaScript
- Homepage: https://github.com/stdlib-js/stdlib
- Size: 603 KB
- Stars: 1
- Watchers: 3
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- Contributing: CONTRIBUTING.md
- License: LICENSE
- Code of conduct: CODE_OF_CONDUCT.md
- Citation: CITATION.cff
- Security: SECURITY.md
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README
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# fromInt64Bytes
[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url]
> Convert a signed 64-bit integer byte array to a [double-precision floating-point number][ieee754].
## Installation
```bash
npm install @stdlib/number-float64-base-from-int64-bytes
```
Alternatively,
- To load the package in a website via a `script` tag without installation and bundlers, use the [ES Module][es-module] available on the [`esm`][esm-url] branch (see [README][esm-readme]).
- If you are using Deno, visit the [`deno`][deno-url] branch (see [README][deno-readme] for usage intructions).
- For use in Observable, or in browser/node environments, use the [Universal Module Definition (UMD)][umd] build available on the [`umd`][umd-url] branch (see [README][umd-readme]).
The [branches.md][branches-url] file summarizes the available branches and displays a diagram illustrating their relationships.
To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.
## Usage
```javascript
var fromInt64Bytes = require( '@stdlib/number-float64-base-from-int64-bytes' );
```
#### fromInt64Bytes( bytes, stride, offset )
Converts a signed 64-bit integer byte array to a [double-precision floating-point number][ieee754].
```javascript
var Uint8Array = require( '@stdlib/array-uint8' );
var bytes = new Uint8Array( [ 255, 255, 255, 255, 255, 255, 255, 255 ] );
var out = fromInt64Bytes( bytes, 1, 0 );
// returns -1.0
```
The function supports providing a `stride` and an index `offset` for indexing into a provided byte array.
```javascript
var Uint8Array = require( '@stdlib/array-uint8' );
var bytes = new Uint8Array( [ 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255 ] );
var out = fromInt64Bytes( bytes, 2, 1 );
// returns -1.0
```
## Notes
- The function assumes host byte order (endianness).
## Examples
```javascript
var IS_LITTLE_ENDIAN = require( '@stdlib/assert-is-little-endian' );
var discreteUniform = require( '@stdlib/random-base-discrete-uniform' );
var bernoulli = require( '@stdlib/random-base-bernoulli' );
var Uint8Array = require( '@stdlib/array-uint8' );
var fromInt64Bytes = require( '@stdlib/number-float64-base-from-int64-bytes' );
var bytes;
var sgn;
var x;
var b;
var s;
var i;
var j;
var k;
bytes = new Uint8Array( 8 );
if ( IS_LITTLE_ENDIAN ) {
k = 0;
s = 1;
} else {
k = 7;
s = -1;
}
// Generate random integer-valued doubles on the interval (-2^16, 2^16)...
for ( i = 0; i < 10; i++ ) {
// Determine the sign:
sgn = ( bernoulli( 0.5 ) ) ? 0 : 128; // 2^7
// Set a subset of individual (lower-order) bytes:
for ( j = 0; j < 2; j++ ) {
b = discreteUniform( 0, 255 ); // 2^8-1
bytes[ k+(j*s) ] = b;
}
// Set higher-order bytes using two's complement:
for ( j = 2; j < 8; j++ ) {
bytes[ k+(j*s) ] = ( sgn ) ? 255 : 0; // 2^8-1
}
// Convert the bytes to a double:
x = fromInt64Bytes( bytes, 1, 0 );
console.log( bytes + ' => ' + x );
}
```
* * *
## See Also
- [`@stdlib/number-float64/base/to-int64-bytes`][@stdlib/number/float64/base/to-int64-bytes]: convert an integer-valued double-precision floating-point number to a signed 64-bit integer byte array according to host byte order.
* * *
## 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 © 2016-2025. The Stdlib [Authors][stdlib-authors].
[npm-image]: http://img.shields.io/npm/v/@stdlib/number-float64-base-from-int64-bytes.svg
[npm-url]: https://npmjs.org/package/@stdlib/number-float64-base-from-int64-bytes
[test-image]: https://github.com/stdlib-js/number-float64-base-from-int64-bytes/actions/workflows/test.yml/badge.svg?branch=main
[test-url]: https://github.com/stdlib-js/number-float64-base-from-int64-bytes/actions/workflows/test.yml?query=branch:main
[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/number-float64-base-from-int64-bytes/main.svg
[coverage-url]: https://codecov.io/github/stdlib-js/number-float64-base-from-int64-bytes?branch=main
[chat-image]: https://img.shields.io/gitter/room/stdlib-js/stdlib.svg
[chat-url]: https://app.gitter.im/#/room/#stdlib-js_stdlib:gitter.im
[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-from-int64-bytes/tree/deno
[deno-readme]: https://github.com/stdlib-js/number-float64-base-from-int64-bytes/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/number-float64-base-from-int64-bytes/tree/umd
[umd-readme]: https://github.com/stdlib-js/number-float64-base-from-int64-bytes/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/number-float64-base-from-int64-bytes/tree/esm
[esm-readme]: https://github.com/stdlib-js/number-float64-base-from-int64-bytes/blob/esm/README.md
[branches-url]: https://github.com/stdlib-js/number-float64-base-from-int64-bytes/blob/main/branches.md
[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/number-float64-base-from-int64-bytes/main/LICENSE
[ieee754]: https://en.wikipedia.org/wiki/IEEE_754-1985
[@stdlib/number/float64/base/to-int64-bytes]: https://github.com/stdlib-js/number-float64-base-to-int64-bytes