code: function flipsign( x, y ) {
  	var hx;
  	var hy;
  
  	// Split `x` into higher and lower order words:
  	x = toWords( x );
  	hx = x[ 0 ];
  
  	// Extract the higher order word from `y`:
  	hy = getHighWord( y );
  
  	// Leave only the sign bit of `y` turned on (if on):
  	hy &= SIGN_MASK;
  
  	// Flip the sign bit of `x` only when the sign bit of `y` is on:
  	hx ^= hy; // 1^1=0 (flipped), 0^1=1 (flipped), 1^0=1 (unchanged), 0^0=0 (unchanged)
  
  	// Return a new value having the same magnitude as `x`, but with the sign of `x*y`:
  	return fromWords( hx, x[ 1 ] );
  }
docs: FLIPSIGN // 
  FUNCTION: flipsign( x, y )
  Returns a double-precision floating-point number with the magnitude of `x` and the sign of `x*y`.
  
  @param {Number} x - number from which to derive a magnitude
  @param {Number} y - number from which to derive a sign
  @returns {Number} a double-precision floating-point number