About stdlib...

We believe in a future in which the web is a preferred environment for numerical computation. To help realize this future, we've built stdlib. stdlib is a standard library, with an emphasis on numerical and scientific computation, written in JavaScript (and C) for execution in browsers and in Node.js.

The library is fully decomposable, being architected in such a way that you can swap out and mix and match APIs and functionality to cater to your exact preferences and use cases.

When you use stdlib, you can be absolutely certain that you are using the most thorough, rigorous, well-written, studied, documented, tested, measured, and high-quality code out there.

To join us in bringing numerical computing to the web, get started by checking us out on GitHub, and please consider financially supporting stdlib. We greatly appreciate your continued support!

Set Low Word

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

Installation

npm install @stdlib/number-float64-base-set-low-word

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

Usage

var setLowWord = require( '@stdlib/number-float64-base-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 ); // => 0 11010011100 01001000001011000011 00000000000000000000000000000101
// returns 3.139998651394392e+201

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( '@stdlib/constants-float64-pinf' );
var NINF = require( '@stdlib/constants-float64-ninf' );

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( '@stdlib/math-base-special-pow' );
var round = require( '@stdlib/math-base-special-round' );
var randu = require( '@stdlib/random-base-randu' );
var MAX_UINT32 = require( '@stdlib/constants-uint32-max' );
var setLowWord = require( '@stdlib/number-float64-base-set-low-word' );

var frac;
var exp;
var low;
var x;
var y;
var i;

// Generate a random double-precision floating-point number:
frac = randu() * 10.0;
exp = -round( randu() * 323.0 );
x = frac * pow( 10.0, 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( randu()*MAX_UINT32 );
    y = setLowWord( x, low );
    console.log( 'x: %d. new low word: %d. y: %d.', x, low, y );
}

---

C APIs

Usage

#include "stdlib/number/float64/base/set_low_word.h"

stdlib_base_float64_set_low_word( low, *x )

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

#include <stdint.h>

uint32_t low = 1374389537;
double x = 3.14;

stdlib_base_float64_set_low_word( low, &x );

The function accepts the following arguments:

• low: [in] uint32_t lower order word.
• x: [in-out] double* reference to (and destination for) a double-precision floating-point number.

void stdlib_base_float64_set_low_word( const uint32_t low, double *x );

Examples

#include "stdlib/number/float64/base/set_low_word.h"
#include <stdint.h>
#include <stdio.h>

int main( void ) {
    uint32_t low[] = { 1374389535, 1374389545, 1374389555, 1374389565 };
    double x = 3.14;

    int i;
    for ( i = 0; i < 4; i++ ) {
        stdlib_base_float64_set_low_word( low[ i ], &x );
        printf( "low: %u => %.15lf\n", low[ i ], x );
    }
}

---

See Also

• @stdlib/number-float64/base/get-low-word: return an unsigned 32-bit integer corresponding to the less significant 32 bits of a double-precision floating-point number.
• @stdlib/number-float64/base/set-high-word: set the more significant 32 bits of a double-precision floating-point number.

---

Notice

This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

Community

---

License

See LICENSE.

Copyright

Copyright © 2016-2025. The Stdlib Authors.