Multiplies a double-precision floating-point number by an integer power of two.
npm install math-float64-ldexpldexp
===
[![NPM version][npm-image]][npm-url] [![Build Status][build-image]][build-url] [![Coverage Status][coverage-image]][coverage-url] [![Dependencies][dependencies-image]][dependencies-url]
> Multiplies a [double-precision floating-point number][ieee754] by an integer power of two.
`` bash`
$ npm install math-float64-ldexp
` javascript`
var ldexp = require( 'math-float64-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 23 = 0.5 8
// returns 4
x = ldexp( 4, -2 ); // => 4 2(-2) = 4 (1/4)
// returns 1
`
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, 20 );
// returns 0
x = ldexp( -0, 39 );
// returns -0
x = ldexp( NaN, -101 );
// returns NaN
x = ldexp( Number.POSITIVE_INFINITY, 11 );
// returns +infinity
x = ldexp( Number.NEGATIVE_INFINITY, -118 );
// returns -infinity
`
* This function is the inverse of [frexp][math-float64-frexp].
` javascript
var round = require( 'math-round' );
var pow = require( 'math-power' );
var frexp = require( 'math-float64-frexp' );
var ldexp = require( 'math-float64-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 ( Math.random() < 0.5 ) {
sign = -1;
} else {
sign = 1;
}
frac = Math.random() * 10;
exp = round( Math.random()*616 ) - 308;
x = sign frac pow( 10, exp );
f = frexp( x );
v = ldexp( f[ 0 ], f[ 1 ] );
console.log( '%d = %d * 2^%d = %d', x, f[ 0 ], f[ 1 ], v );
}
`
To run the example code from the top-level application directory,
` bash`
$ node ./examples/index.js
---
This repository uses [tape][tape] for unit tests. To run the tests, execute the following command in the top-level application directory:
` bash`
$ make test
All new feature development should have corresponding unit tests to validate correct functionality.
This repository uses [Istanbul][istanbul] as its code coverage tool. To generate a test coverage report, execute the following command in the top-level application directory:
` bash`
$ make test-cov
Istanbul creates a ./reports/coverage directory. To access an HTML version of the report,
` bash`
$ make view-cov
This repository uses [Testling][testling] for browser testing. To run the tests in a (headless) local web browser, execute the following command in the top-level application directory:
` bash`
$ make test-browsers
To view the tests in a local web browser,
` bash``
$ make view-browser-tests
---
Copyright © 2016. The [Compute.io][compute-io] Authors.
[npm-image]: http://img.shields.io/npm/v/math-float64-ldexp.svg
[npm-url]: https://npmjs.org/package/math-float64-ldexp
[build-image]: http://img.shields.io/travis/math-io/float64-ldexp/master.svg
[build-url]: https://travis-ci.org/math-io/float64-ldexp
[coverage-image]: https://img.shields.io/codecov/c/github/math-io/float64-ldexp/master.svg
[coverage-url]: https://codecov.io/github/math-io/float64-ldexp?branch=master
[dependencies-image]: http://img.shields.io/david/math-io/float64-ldexp.svg
[dependencies-url]: https://david-dm.org/math-io/float64-ldexp
[dev-dependencies-image]: http://img.shields.io/david/dev/math-io/float64-ldexp.svg
[dev-dependencies-url]: https://david-dm.org/dev/math-io/float64-ldexp
[github-issues-image]: http://img.shields.io/github/issues/math-io/float64-ldexp.svg
[github-issues-url]: https://github.com/math-io/float64-ldexp/issues
[tape]: https://github.com/substack/tape
[istanbul]: https://github.com/gotwarlost/istanbul
[testling]: https://ci.testling.com
[compute-io]: https://github.com/compute-io/
[ieee754]: https://en.wikipedia.org/wiki/IEEE_754-1985
[math-float64-frexp]: https://github.com/math-io/float64-frexp