## Usage ```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 ```

## Notes - This function is the inverse of [`frexp`][@stdlib/math/base/special/frexp].

## Examples ```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; /* * 1) Generate random numbers. * 2) Break each number into a normalized fraction and an integer power of two. * 3) Reconstitute the original number. */ for ( i = 0; i < 100; i++ ) { if ( randu() < 0.5 ) { sign = -1.0; } else { sign = 1.0; } frac = randu() * 10.0; exp = round( randu()*616.0 ) - 308; x = sign * frac * pow( 10.0, exp ); f = frexp( x ); v = ldexp( f[ 0 ], f[ 1 ] ); console.log( '%d = %d * 2^%d = %d', x, f[ 0 ], f[ 1 ], v ); } ```

[ieee754]: https://en.wikipedia.org/wiki/IEEE_754-1985 [@stdlib/math/base/special/frexp]: https://www.npmjs.com/package/@stdlib/math/tree/main/base/special/frexp