Multiply a double-precision floating-point number by an integer power of two.
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> Multiply a [double-precision floating-point number][ieee754] by an integer power of two.
``bash`
npm install @stdlib/math-base-special-ldexp
`javascript`
var ldexp = require( '@stdlib/math-base-special-ldexp' );
#### ldexp( frac, exp )
Multiplies a [double-precision floating-point number][ieee754] by an integer power of two (i.e., x = frac * 2^exp).
`javascript
var x = ldexp( 0.5, 3 ); // => 0.5 2^3 = 0.5 8
// returns 4.0
x = ldexp( 4.0, -2 ); // => 4 2^(-2) = 4 (1/4)
// returns 1.0
`
If frac equals positive or negative zero, NaN, or positive or negative infinity, the function returns a value equal to frac.
`javascript
var x = ldexp( 0.0, 20 );
// returns 0.0
x = ldexp( -0.0, 39 );
// returns -0.0
x = ldexp( NaN, -101 );
// returns NaN
x = ldexp( Infinity, 11 );
// returns Infinity
x = ldexp( -Infinity, -118 );
// returns -Infinity
`
- This function is the inverse of [frexp][@stdlib/math/base/special/frexp].
`javascript
var randu = require( '@stdlib/random-base-randu' );
var round = require( '@stdlib/math-base-special-round' );
var pow = require( '@stdlib/math-base-special-pow' );
var frexp = require( '@stdlib/math-base-special-frexp' );
var ldexp = require( '@stdlib/math-base-special-ldexp' );
var sign;
var frac;
var exp;
var x;
var f;
var v;
var i;
for ( i = 0; i < 100; i++ ) {
if ( randu() < 0.5 ) {
sign = -1.0;
} else {
sign = 1.0;
}
// Generate a random number:
frac = randu() * 10.0;
exp = round( randu()*616.0 ) - 308;
x = sign frac pow( 10.0, exp );
// Break the number into a normalized fraction and an integer power of two:
f = frexp( x );
// Reconstitute the original number:
v = ldexp( f[ 0 ], f[ 1 ] );
console.log( '%d = %d * 2^%d = %d', x, f[ 0 ], f[ 1 ], v );
}
`
*
`c`
#include "stdlib/math/base/special/ldexp.h"
#### stdlib_base_ldexp( frac, exp )
Multiplies a [double-precision floating-point number][ieee754] by an integer power of two (i.e., x = frac * 2^exp).
`c`
double x = stdlib_base_ldexp( 0.5, 3 ); // => 0.5 2^3 = 0.5 8
// returns 4.0
The function accepts the following arguments:
- frac: [in] double input value.[in] int32_t
- exp: integer power of two.
`c`
double stdlib_base_ldexp( const double frac, const int32_t exp );
`c
#include "stdlib/math/base/special/ldexp.h"
#include
#include
int main( void ) {
double y;
int i;
const double frac[] = { 0.5, 5.0, 0.0, 3.5, 7.9 };
const int32_t exp[] = { 3, -2, 20, 39, 14 };
for ( i = 0; i < 5; i++ ) {
y = stdlib_base_ldexp( frac[ i ], exp[ i ] );
printf( "ldexp(%lf, %d) = %lf\n", frac[ i ], exp[ i ], y );
}
}
`
*
- [@stdlib/math-base/special/frexp][@stdlib/math/base/special/frexp]: split a double-precision floating-point number into a normalized fraction and an integer power of two.
*
This package is part of [stdlib][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][stdlib], see the main project [repository][stdlib].
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---
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Copyright © 2016-2026. The Stdlib [Authors][stdlib-authors].
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[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules
[deno-url]: https://github.com/stdlib-js/math-base-special-ldexp/tree/deno
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[@stdlib/math/base/special/frexp]: https://www.npmjs.com/package/@stdlib/math-base-special-frexp