stdlib-js
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ldexp
[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url]
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
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.
- exp: [in] int32_t 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 "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 );
}
}
@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.
