# @stdlib/number-float64-base-set-low-word

0.2.2 • Public • Published

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# 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`

## 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 );
}
}```

## 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.

## Package Sidebar

### Install

`npm i @stdlib/number-float64-base-set-low-word`

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