math-float64-set-low-word

Set Low Word

Sets the less significant 32 bits of a double-precision floating-point number.

Installation

$ npm install math-float64-set-low-word

Usage

var setLowWord = require( 'math-float64-set-low-word' );

setLowWord( x, low )

Sets the less significant 32 bits (lower order word) of a double-precision floating-point number x to a bit sequence represented by an unsigned 32-bit integer low. The returned double will have the same more significant 32 bits (higher order word) as x.

var low = 5 >>> 0;
// => 00000000000000000000000000000101
 
var x = 3.14e201;
// => 0 11010011100 01001000001011000011 10010011110010110101100010000010
 
var y = setLowWord( x, low );
// returns 3.139998651394392e+201 => 0 11010011100 01001000001011000011 00000000000000000000000000000101

Setting the lower order bits of NaN or positive or negative infinity will return NaN, as NaN is defined as a double whose exponent bit sequence is all ones and whose fraction can be any bit sequence except all zeros. Positive and negative infinity are defined as doubles with an exponent bit sequence equal to all ones and a fraction equal to all zeros. Hence, changing the less significant bits of positive and negative infinity converts each value to NaN.

var pinf = require( 'const-pinf-float64' );
var ninf = require( 'const-ninf-float64' );
 
var low = 12345678;
 
var y = setLowWord( pinf, low );
// returns NaN  
 
y = setLowWord( ninf, low );
// returns NaN
 
y = setLowWord( NaN, low );
// returns NaN

Examples

var pow = require( 'math-power' );
var round = require( 'math-round' );
var setLowWord = require( 'math-float64-set-low-word' );
 
var MAX_UINT;
var frac;
var exp;
var low;
var x;
var y;
var i;
 
// Max unsigned 32-bit integer:
MAX_UINT = pow( 2, 32 ) - 1;
 
// Generate a random double-precision floating-point number:
frac = Math.random() * 10;
exp = -round( Math.random() * 323 );
x = frac * pow( 10, exp );
 
// Replace the lower order word of `x` to generate new random numbers having the same higher order word...
for ( i = 0; i < 100; i++ ) {
    low = round( Math.random()*MAX_UINT );
    y = setLowWord( x, low );
    console.log( 'x: %d. new low word: %d. y: %d.', x, low, y );
}

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.