npm package: @stdlib/math-base-special-flipsign
Description: Return a double-precision floating-point number with the magnitude of x and the sign of x*y.
Author: The Stdlib Authors
Latest version: 0.2.3

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# flipsign

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

> Return a [double-precision floating-point number][ieee754] with the magnitude of `x` and the sign of `x*y`.

<section class="installation">

## Installation

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

</section>

<section class="usage">

## Usage

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

#### flipsign( x, y )

Returns a [double-precision floating-point number][ieee754] with the magnitude of `x` and the sign of `x*y` (i.e., only return `-x` when `y` is a negative number).

```javascript
var z = flipsign( -3.0, 10.0 );
// returns -3.0

z = flipsign( -3.0, -1.0 );
// returns 3.0

z = flipsign( 1.0, -0.0 );
// returns -1.0

z = flipsign( -3.0, -0.0 );
// returns 3.0

z = flipsign( -0.0, 1.0 );
// returns -0.0

z = flipsign( 0.0, -1.0 );
// returns -0.0
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   According to the [IEEE 754][ieee754] standard, a `NaN` has a biased exponent equal to `2047`, a significand greater than `0`, and a sign bit equal to **either** `1` **or** `0`. In which case, `NaN` may not correspond to just one but many binary representations. Accordingly, care should be taken to ensure that `y` is **not** `NaN`; otherwise, behavior may be indeterminate.

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var uniform = require( '@stdlib/random-array-uniform' );
var logEachMap = require( '@stdlib/console-log-each-map' );
var flipsign = require( '@stdlib/math-base-special-flipsign' );

var opts = {
    'dtype': 'float64'
};
var x = uniform( 100, -50.0, 50.0, opts );
var y = uniform( 100, -5.0, 5.0, opts );

// Generate random numbers `x` and `y` and flip the sign of `x` only if `y` is negative...
logEachMap( 'x: %0.4f, y: %0.4f => %0.4f', x, y, flipsign );
```

</section>

<!-- /.examples -->

<!-- C interface documentation. -->

* * *

<section class="c">

## C APIs

<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->

<section class="intro">

</section>

<!-- /.intro -->

<!-- C usage documentation. -->

<section class="usage">

### Usage

```c
#include "stdlib/math/base/special/flipsign.h"
```

#### stdlib_base_flipsign( x, y )

Returns a [double-precision floating-point number][ieee754] with the magnitude of `x` and the sign of `x*y`.

```c
double v = stdlib_base_flipsign( -3.0, 10.0 );
// returns -3.0

v = stdlib_base_flipsign( -3.0, -1.0 );
// returns 3.0
```

The function accepts the following arguments:

-   **x**: `[in] double` number from which to derive a magnitude.
-   **y**: `[in] double` number from which to derive a sign.

```c
double stdlib_base_flipsign( const double x, const double y );
```

</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/flipsign.h"
#include <stdio.h>

int main( void ) {
    const double x[] = { 3.0, -3.0, 0.0, 0.0/0.0 };

    double y;
    int i;
    for ( i = 0; i < 4; i++ ) {
        y = stdlib_base_flipsign( x[ i ], -3.0 );
        printf( "flipsign(%lf, %lf) = %lf\n", x[ i ], -3.0, y );
    }
}
```

</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/copysign`][@stdlib/math/base/special/copysign]</span><span class="delimiter">: </span><span class="description">return a double-precision floating-point number with the magnitude of x and the sign of y.</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

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---

## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

</section>

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[umd]: https://github.com/umdjs/umd
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[ieee754]: https://en.wikipedia.org/wiki/IEEE_754-1985

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

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</section>

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