flipsign

Return a double-precision floating-point number with the magnitude of x and the sign of x*y.

Usage

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

flipsign( x, y )

Returns a double-precision floating-point number with the magnitude of x and the sign of x*y (i.e., only return -x when y is a negative number).

var z = flipsign( -3.0, 10.0 );
// returns -3.0

z = flipsign( -3.0, -1.0 );
// returns 3.0

z = flipsign( 1.0, -0.0 );
// returns -1.0

z = flipsign( -3.0, -0.0 );
// returns 3.0

z = flipsign( -0.0, 1.0 );
// returns -0.0

z = flipsign( 0.0, -1.0 );
// returns -0.0

Notes

According to the IEEE 754 standard, a NaN has a biased exponent equal to 2047, a significand greater than 0, and a sign bit equal to either 1 or 0. In which case, NaN may not correspond to just one but many binary representations. Accordingly, care should be taken to ensure that y is not NaN; otherwise, behavior may be indeterminate.

Examples

var randu = require( '@stdlib/random/base/randu' );
var flipsign = require( '@stdlib/math/base/special/flipsign' );

var x;
var y;
var z;
var i;

// Generate random numbers `x` and `y` and flip the sign of `x` only if `y` is negative...
for ( i = 0; i < 100; i++ ) {
    x = (randu()*100.0) - 50.0;
    y = (randu()*10.0) - 5.0;
    z = flipsign( x, y );
    console.log( 'x: %d, y: %d => %d', x, y, z );
}

C APIs

Usage

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

stdlib_base_flipsign( x, y )

Returns a double-precision floating-point number with the magnitude of x and the sign of x*y.

double v = stdlib_base_flipsign( -3.0, 10.0 );
// returns -3.0

double v = stdlib_base_flipsign( -3.0, -1.0 );
// returns 3.0

The function accepts the following arguments:

x: [in] double number from which to derive a magnitude.
y: [in] double number from which to derive a sign.

double stdlib_base_flipsign( const double x, const double y );

Examples

#include "stdlib/math/base/special/flipsign.h"
#include <stdio.h>

int main( void ) {
    const double x[] = { 3.0, -3.0, 0.0, 0.0/0.0 };

    double y;
    int i;
    for ( i = 0; i < 4; i++ ) {
        y = stdlib_base_flipsign( x[ i ], -3.0 );
        printf( "flipsign(%lf, %lf) = %lf\n", x[ i ], -3.0, y );
    }
}