function signbitf( x ) {
	// Convert `x` to an unsigned 32-bit integer corresponding to the value's IEEE 754 binary representation:
	var w = toWord( x );

	// Shift off all bits which are not the sign bit and check if the sign bit is on:
	return ( w >>> 31 ) ? true : false; // eslint-disable-line no-unneeded-ternary
}
Returns a boolean indicating if the sign bit is on (true) or off (false).

@param {number} x - single-precision floating-point number
@returns {boolean} boolean indicating if sign bit is on or off

@example
var toFloat32 = require( '@stdlib/number/float64/base/to-float32' );

var bool = signbitf( toFloat32( 4.0 ) );
// returns false

@example
var toFloat32 = require( '@stdlib/number/float64/base/to-float32' );

var bool = signbitf( toFloat32( -9.14e-34 ) );
// returns true

@example
var bool = signbitf( 0.0 );
// returns false

@example
var bool = signbitf( -0.0 );
// returns true