npm package: @stdlib/math-base-special-ldexp
Description: Multiply a double-precision floating-point number by an integer power of two.
Author: The Stdlib Authors
Latest version: 0.2.5

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# ldexp

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

> Multiply a [double-precision floating-point number][ieee754] by an integer power of two.

<section class="installation">

## Installation

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

</section>

<section class="usage">

## Usage

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

#### ldexp( frac, exp )

Multiplies a [double-precision floating-point number][ieee754] by an `integer` power of two (i.e., `x = frac * 2^exp`).

```javascript
var x = ldexp( 0.5, 3 ); // => 0.5 * 2^3 = 0.5 * 8
// returns 4.0

x = ldexp( 4.0, -2 ); // => 4 * 2^(-2) = 4 * (1/4)
// returns 1.0
```

If `frac` equals positive or negative zero, `NaN`, or positive or negative `infinity`, the function returns a value equal to `frac`.

```javascript
var x = ldexp( 0.0, 20 );
// returns 0.0

x = ldexp( -0.0, 39 );
// returns -0.0

x = ldexp( NaN, -101 );
// returns NaN

x = ldexp( Infinity, 11 );
// returns Infinity

x = ldexp( -Infinity, -118 );
// returns -Infinity
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   This function is the inverse of [`frexp`][@stdlib/math/base/special/frexp].

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var randu = require( '@stdlib/random-base-randu' );
var round = require( '@stdlib/math-base-special-round' );
var pow = require( '@stdlib/math-base-special-pow' );
var frexp = require( '@stdlib/math-base-special-frexp' );
var ldexp = require( '@stdlib/math-base-special-ldexp' );

var sign;
var frac;
var exp;
var x;
var f;
var v;
var i;

for ( i = 0; i < 100; i++ ) {
    if ( randu() < 0.5 ) {
        sign = -1.0;
    } else {
        sign = 1.0;
    }
    // Generate a random number:
    frac = randu() * 10.0;
    exp = round( randu()*616.0 ) - 308;
    x = sign * frac * pow( 10.0, exp );

    // Break the number into a normalized fraction and an integer power of two:
    f = frexp( x );

    // Reconstitute the original number:
    v = ldexp( f[ 0 ], f[ 1 ] );
    console.log( '%d = %d * 2^%d = %d', x, f[ 0 ], f[ 1 ], v );
}
```

</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/ldexp.h"
```

#### stdlib_base_ldexp( frac, exp )

Multiplies a [double-precision floating-point number][ieee754] by an integer power of two (i.e., `x = frac * 2^exp`).

```c
double x = stdlib_base_ldexp( 0.5, 3 ); // => 0.5 * 2^3 = 0.5 * 8
// returns 4.0
```

The function accepts the following arguments:

-   **frac**: `[in] double` input value.
-   **exp**: `[in] int32_t` integer power of two.

```c
double stdlib_base_ldexp( const double frac, const int32_t exp );
```

</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/ldexp.h"
#include <stdint.h>
#include <stdio.h>

int main( void ) {
    double y;
    int i;

    const double frac[] = { 0.5, 5.0, 0.0, 3.5, 7.9 };
    const int32_t exp[] = { 3, -2, 20, 39, 14 };

    for ( i = 0; i < 5; i++ ) {
        y = stdlib_base_ldexp( frac[ i ], exp[ i ] );
        printf( "ldexp(%lf, %d) = %lf\n", frac[ i ], exp[ i ], 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/frexp`][@stdlib/math/base/special/frexp]</span><span class="delimiter">: </span><span class="description">split a double-precision floating-point number into a normalized fraction and an integer power of two.</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].

</section>

<!-- /.stdlib -->

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[deno-url]: https://github.com/stdlib-js/math-base-special-ldexp/tree/deno
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[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/math-base-special-ldexp/main/LICENSE

[ieee754]: https://en.wikipedia.org/wiki/IEEE_754-1985

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

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</section>

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