Nabbing Pleasant Monads

    math-float64-frexp

    1.0.0 • Public • Published

    frexp

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    Splits a double-precision floating-point number into a normalized fraction and an integer power of two.

    Installation

    $ npm install math-float64-frexp

    Usage

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

    frexp( x )

    Splits a double-precision floating-point number into a normalized fraction and an integer power of two.

    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.

    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.

    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 of the normalized fraction resides on the interval [1/2,1).

    Notes

    • Care should be taken when reconstituting a double-precision floating-point number from a normalized fraction and an exponent. For example,

      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 2**1024 evaluating as infinity by recognizing 2**1024 = 2**1 * 2**1023:
      = out[ 0 ] * pow( 2, out[1]-1023 ) * pow( 2, 1023 );
      // returns 8.988939926493918e+307

    Examples

    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,

    $ node ./examples/index.js

    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

    License

    MIT license.

    Copyright

    Copyright © 2016. The Compute.io Authors.

    Install

    npm i math-float64-frexp

    DownloadsWeekly Downloads

    507

    Version

    1.0.0

    License

    MIT

    Last publish

    Collaborators

    • kgryte