Splits a double-precision floating-point number into a normalized fraction and an integer power of two.
npm install math-float64-frexpfrexp
===
[![NPM version][npm-image]][npm-url] [![Build Status][build-image]][build-url] [![Coverage Status][coverage-image]][coverage-url] [![Dependencies][dependencies-image]][dependencies-url]
> Splits a [double-precision floating-point number][ieee754] into a normalized fraction and an integer power of two.
`` bash`
$ npm install math-float64-frexp
` javascript`
var frexp = require( 'math-float64-frexp' );
#### frexp( x )
Splits a [double-precision floating-point number][ieee754] into a normalized fraction and an integer power of two.
` javascript`
var out = frexp( 4 );
// returns [ 0.5, 3 ]
The first element of the returned array is the normalized fraction and the second is the exponent. The normalized fraction and exponent satisfy the relation x = frac 2*exp.
` javascript
var pow = require( 'math-power' );
var x = 4;
var out = frexp( x );
// returns [ 0.5, 3 ]
var frac = out[ 0 ];
var exp = out[ 1 ];
var bool = ( x === frac * pow(2,exp) );
// returns true
`
If provided positive or negative zero, NaN, or positive or negative infinity, the function returns a two-element array containing the input value and an exponent equal to 0.
` javascript
var out = frexp( 0 );
// returns [ 0, 0 ]
out = frexp( -0 );
// returns [ -0, 0 ]
out = frexp( NaN );
// returns [ NaN, 0 ]
out = frexp( Number.POSITIVE_INFINITY );
// returns [ +infinity, 0 ]
out = frexp( Number.NEGATIVE_INFINITY );
// returns [ -infinity, 0 ]
`
For all other numeric input values, the [absolute value][math-abs] of the normalized fraction resides on the interval [1/2,1).
* Care should be taken when reconstituting a [double-precision floating-point number][ieee754] from a normalized fraction and an exponent. For example,
` javascript
var pow = require( 'math-power' );
// x ~ 2**1023
var x = 8.988939926493918e+307;
var out = frexp( x );
// returns [ 0.5000263811533315, 1024 ]
// Naive reconstitution:
var y = out[ 0 ] * pow( 2, out[ 1 ] );
// returns +infinity
// Account for 21024 evaluating as infinity by recognizing 21024 = 21 * 21023:
y = out[ 0 ] pow( 2, out[1]-1023 ) pow( 2, 1023 );
// returns 8.988939926493918e+307
`
` javascript
var round = require( 'math-round' );
var pow = require( 'math-power' );
var frexp = require( 'math-float64-frexp' );
var sign;
var frac;
var exp;
var x;
var f;
var v;
var i;
// Generate random numbers and break each into a normalized fraction and an integer power of two...
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 );
if ( f[ 1 ] > 1023 ) {
v = f[ 0 ] pow( 2, f[1]-1023 ) pow( 2, 1023 );
} else {
v = f[ 0 ] * pow( 2, 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-frexp.svg
[npm-url]: https://npmjs.org/package/math-float64-frexp
[build-image]: http://img.shields.io/travis/math-io/float64-frexp/master.svg
[build-url]: https://travis-ci.org/math-io/float64-frexp
[coverage-image]: https://img.shields.io/codecov/c/github/math-io/float64-frexp/master.svg
[coverage-url]: https://codecov.io/github/math-io/float64-frexp?branch=master
[dependencies-image]: http://img.shields.io/david/math-io/float64-frexp.svg
[dependencies-url]: https://david-dm.org/math-io/float64-frexp
[dev-dependencies-image]: http://img.shields.io/david/dev/math-io/float64-frexp.svg
[dev-dependencies-url]: https://david-dm.org/dev/math-io/float64-frexp
[github-issues-image]: http://img.shields.io/github/issues/math-io/float64-frexp.svg
[github-issues-url]: https://github.com/math-io/float64-frexp/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-abs]: https://github.com/math-io/abs