ldexp

Multiplies a double-precision floating-point number by an integer power of two.

Installation

$ npm install math-float64-ldexp

Usage

var ldexp = require( 'math-float64-ldexp' );

ldexp( frac, exp )

Multiplies a double-precision floating-point number by an integer power of two; i.e., x = frac * 2**exp.

var x = ldexp( 0.5, 3 ); // => 0.5 * 2**3 = 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.

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

Notes

• This function is the inverse of frexp.

Examples

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,

$ node ./examples/index.js

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Tests

Unit

This repository uses tape for unit tests. To run the tests, execute the following command in the top-level application directory:

$ make test

All new feature development should have corresponding unit tests to validate correct functionality.

Test Coverage

This repository uses Istanbul as its code coverage tool. To generate a test coverage report, execute the following command in the top-level application directory:

$ make test-cov

Istanbul creates a ./reports/coverage directory. To access an HTML version of the report,

$ make view-cov

Browser Support

This repository uses Testling for browser testing. To run the tests in a (headless) local web browser, execute the following command in the top-level application directory:

$ make test-browsers

To view the tests in a local web browser,

$ make view-browser-tests

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License

MIT license.

Copyright

Copyright © 2016. The Compute.io Authors.