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Set the less significant 32 bits of a doubleprecision floatingpoint number.
npm install @stdlib/numberfloat64basesetlowword
var setLowWord = require( '@stdlib/numberfloat64basesetlowword' );
Sets the less significant 32 bits (lower order word) of a doubleprecision floatingpoint number x
to a bit sequence represented by an unsigned 32bit 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/constantsfloat64pinf' );
var NINF = require( '@stdlib/constantsfloat64ninf' );
var low = 12345678;
var y = setLowWord( PINF, low );
// returns NaN
y = setLowWord( NINF, low );
// returns NaN
y = setLowWord( NaN, low );
// returns NaN
var pow = require( '@stdlib/mathbasespecialpow' );
var round = require( '@stdlib/mathbasespecialround' );
var randu = require( '@stdlib/randombaserandu' );
var MAX_UINT32 = require( '@stdlib/constantsuint32max' );
var setLowWord = require( '@stdlib/numberfloat64basesetlowword' );
var frac;
var exp;
var low;
var x;
var y;
var i;
// Generate a random doubleprecision floatingpoint 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 );
}
#include "stdlib/number/float64/base/set_low_word.h"
Sets the less significant 32 bits of a doubleprecision floatingpoint 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:
[inout] double*
reference to (and destination for) a doubleprecision floatingpoint number.
void stdlib_base_float64_set_low_word( const uint32_t low, double *x );
#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 );
}
}

@stdlib/numberfloat64/base/getlowword
: return an unsigned 32bit integer corresponding to the less significant 32 bits of a doubleprecision floatingpoint number. 
@stdlib/numberfloat64/base/sethighword
: set the more significant 32 bits of a doubleprecision floatingpoint number.
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.
See LICENSE.
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