npm package: @stdlib/number-float64-base-to-int64-bytes
Description: Convert an integer-valued double-precision floating-point number to a signed 64-bit integer byte array according to host byte order.
Author: The Stdlib Authors
Latest version: 0.2.3

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# toInt64Bytes

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

> Convert an integer-valued [double-precision floating-point number][ieee754] to a signed 64-bit integer byte array according to host byte order (endianness).

<section class="installation">

## Installation

```bash
npm install @stdlib/number-float64-base-to-int64-bytes
```

</section>

<section class="usage">

## Usage

```javascript
var float64ToInt64Bytes = require( '@stdlib/number-float64-base-to-int64-bytes' );
```

#### float64ToInt64Bytes( x )

Converts an integer-valued [double-precision floating-point number][ieee754] to a signed 64-bit integer byte array according to host byte order (endianness).

```javascript
var out = float64ToInt64Bytes( 4294967297.0 );
// returns <Uint8Array>
```

#### float64ToInt64Bytes.assign( x, out, stride, offset )

Converts an integer-valued [double-precision floating-point number][ieee754] to a signed 64-bit integer byte array according to host byte order (endianness) and assigns results to a provided output array.

```javascript
var Uint8Array = require( '@stdlib/array-uint8' );

var out = new Uint8Array( 16 );
var y = float64ToInt64Bytes.assign( 4294967297.0, out, 2, 1 );
// returns <Uint8Array>

var bool = ( y === out );
// returns true
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   The functions assume that the input value is less than the maximum safe [double-precision floating-point][ieee754] integer plus one (i.e., `2**53`).

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var toBinaryStringUint8 = require( '@stdlib/number-uint8-base-to-binary-string' );
var float64ToInt64Bytes = require( '@stdlib/number-float64-base-to-int64-bytes' );

var bytes;
var str;
var sgn;
var x;
var i;
var j;

str = [ '', '', '', '', '', '', '', '', '' ];
x = 1;

for ( i = 0; i < 54; i++ ) {
    sgn = ( i&1 ) ? -1 : 1;
    bytes = float64ToInt64Bytes( x*sgn );
    for ( j = 0; j < bytes.length; j++ ) {
        str[ j ] = toBinaryStringUint8( bytes[ j ] );
    }
    console.log( '%s2**%d => %s', ( sgn < 0 ) ? '-' : '+', i, str.join( ' ' ) );
    x *= 2;
}
```

</section>

<!-- /.examples -->

<!-- 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/number-float64/base/to-int32`][@stdlib/number/float64/base/to-int32]</span><span class="delimiter">: </span><span class="description">convert a double-precision floating-point number to a signed 32-bit integer.</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

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