ldexp

Multiply a double-precision floating-point number by an integer power of two.

Installation

npm install @stdlib/math-base-special-ldexp

Usage

var ldexp = require( '@stdlib/math-base-special-ldexp' );

ldexp( frac, exp )

Multiplies a double-precision floating-point number by an integer power of two (i.e., x = frac * 2^exp).

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.

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.

Examples

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 APIs

Usage

#include "stdlib/math/base/special/ldexp.h"

stdlib_base_ldexp( frac, exp )

Multiplies a double-precision floating-point number by an integer power of two (i.e., x = frac * 2^exp).

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.
• exp: [in] int32_t integer power of two.

double stdlib_base_ldexp( const double frac, const int32_t exp );

Examples

#include "stdlib/math/base/special/ldexp.h"
#include "stdlib/math/base/special/frexp.h"
#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>
#include <inttypes.h>
#include <math.h>

static double rand_double() {
    int r = rand();
    return (double)r / ( (double)RAND_MAX + 1.0 );
}

int main( void ) {
    double sign;
    double frac;
    int32_t exp;
    double x;
    double v;
    int i;

    for ( i = 0; i < 100; i++ ) {
        if ( rand_double() < 0.5 ) {
            sign = -1.0;
        } else {
            sign = 1.0;
        }
        // Generate a random number:
        frac = rand_double() * 10.0;
        exp = (int32_t)( rand_double()*616.0 ) - 308;
        x = sign * frac * pow( 10.0, exp );

        // Break the number into a normalized fraction and an integer power of two:
        stdlib_base_frexp( x, &frac, &exp );

        // Reconstitute the original number:
        v = stdlib_base_ldexp( frac, exp );

        printf( "%e = %lf * 2^%" PRId32 " = %e\n", x, frac, exp, v );
    }
}

See Also

• @stdlib/math-base/special/frexp: split a double-precision floating-point number into a normalized fraction and an integer power of two.

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.

Community

License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.