Set Low Word

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

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