time-to-botec/js/node_modules/@stdlib/math/base/special/ldexp/README.md

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@license Apache-2.0
Copyright (c) 2018 The Stdlib Authors.
Licensed under the Apache License, Version 2.0 (the "License");
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# ldexp
> Multiply a [double-precision floating-point number][ieee754] by an integer power of two.
<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 class="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;
/*
* 1) Generate random numbers.
* 2) Break each number into a normalized fraction and an integer power of two.
* 3) Reconstitute the original number.
*/
for ( i = 0; i < 100; i++ ) {
if ( randu() < 0.5 ) {
sign = -1.0;
} else {
sign = 1.0;
}
frac = randu() * 10.0;
exp = round( randu()*616.0 ) - 308;
x = sign * frac * pow( 10.0, exp );
f = frexp( x );
v = ldexp( f[ 0 ], f[ 1 ] );
console.log( '%d = %d * 2^%d = %d', x, f[ 0 ], f[ 1 ], v );
}
```
</section>
<!-- /.examples -->
<section class="links">
[ieee754]: https://en.wikipedia.org/wiki/IEEE_754-1985
[@stdlib/math/base/special/frexp]: https://www.npmjs.com/package/@stdlib/math/tree/main/base/special/frexp
</section>
<!-- /.links -->