130 lines
2.8 KiB
Markdown
130 lines
2.8 KiB
Markdown
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@license Apache-2.0
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Copyright (c) 2018 The Stdlib Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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# ldexp
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> Multiply a [double-precision floating-point number][ieee754] by an integer power of two.
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<section class="usage">
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## Usage
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```javascript
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var ldexp = require( '@stdlib/math/base/special/ldexp' );
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```
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#### ldexp( frac, exp )
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Multiplies a [double-precision floating-point number][ieee754] by an `integer` power of two; i.e., `x = frac * 2^exp`.
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```javascript
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var x = ldexp( 0.5, 3 ); // => 0.5 * 2^3 = 0.5 * 8
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// returns 4.0
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x = ldexp( 4.0, -2 ); // => 4 * 2^(-2) = 4 * (1/4)
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// returns 1.0
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```
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If `frac` equals positive or negative `zero`, `NaN`, or positive or negative `infinity`, the function returns a value equal to `frac`.
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```javascript
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var x = ldexp( 0.0, 20 );
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// returns 0.0
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x = ldexp( -0.0, 39 );
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// returns -0.0
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x = ldexp( NaN, -101 );
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// returns NaN
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x = ldexp( Infinity, 11 );
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// returns Infinity
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x = ldexp( -Infinity, -118 );
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// returns -Infinity
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```
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<section class="usage">
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<section class="notes">
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## Notes
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- This function is the inverse of [`frexp`][@stdlib/math/base/special/frexp].
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</section>
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<!-- /.notes -->
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<section class="examples">
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## Examples
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<!-- eslint no-undef: "error" -->
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```javascript
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var randu = require( '@stdlib/random/base/randu' );
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var round = require( '@stdlib/math/base/special/round' );
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var pow = require( '@stdlib/math/base/special/pow' );
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var frexp = require( '@stdlib/math/base/special/frexp' );
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var ldexp = require( '@stdlib/math/base/special/ldexp' );
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var sign;
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var frac;
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var exp;
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var x;
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var f;
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var v;
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var i;
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/*
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* 1) Generate random numbers.
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* 2) Break each number into a normalized fraction and an integer power of two.
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* 3) Reconstitute the original number.
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*/
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for ( i = 0; i < 100; i++ ) {
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if ( randu() < 0.5 ) {
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sign = -1.0;
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} else {
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sign = 1.0;
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}
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frac = randu() * 10.0;
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exp = round( randu()*616.0 ) - 308;
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x = sign * frac * pow( 10.0, exp );
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f = frexp( x );
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v = ldexp( f[ 0 ], f[ 1 ] );
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console.log( '%d = %d * 2^%d = %d', x, f[ 0 ], f[ 1 ], v );
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}
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```
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</section>
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<!-- /.examples -->
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<section class="links">
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[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/tree/main/base/special/frexp
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</section>
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<!-- /.links -->
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