function sqrt1pm1( x ) {
	if ( isnan( x ) ) {
		return NaN;
	}
	if ( abs( x ) > 0.75 ) {
		return sqrt( 1.0+x ) - 1.0;
	}
	return expm1( log1p( x ) / 2.0 );
}
Computes the value of `sqrt(1+x)-1`.

@param {number} x - input value
@returns {number} square root of `1+x` minus one

@example
var v = sqrt1pm1( 3.0 );
// returns 1.0

@example
var v = sqrt1pm1( 0.5 );
// returns ~0.225

@example
var v = sqrt1pm1( 0.02 );
// returns ~0.01

@example
var v = sqrt1pm1( -0.5 );
// returns ~-0.293

@example
var v = sqrt1pm1( -1.1 );
// returns NaN

@example
var v = sqrt1pm1( NaN );
// returns NaN