function fibonacciIndexf( F ) {
	var x;
	if (
		isnanf( F ) ||
		isIntegerf( F ) === false ||
		F <= 1 ||
		F === PINF
	) {
		return NaN;
	}
	x = float64ToFloat32( float64ToFloat32( F*SQRT_5 ) + ONE_HALF );
	return roundf( float64ToFloat32( lnf( x ) / LN_PHI ) );
}
Computes the Fibonacci number index of a single-precision floating-point number.

## Notes

-   We use `roundf` instead of `floorf` due to errors introduced by floating-point precision.

@param {NonNegativeInteger} F - Fibonacci number
@returns {NonNegativeInteger} Fibonacci number index

@example
var n = fibonacciIndexf( 0 );
// returns NaN

@example
var n = fibonacciIndexf( 1 );
// returns NaN

@example
var n = fibonacciIndexf( 2 );
// returns 3

@example
var n = fibonacciIndexf( 3 );
// returns 4

@example
var n = fibonacciIndexf( 5 );
// returns 5

@example
var n = fibonacciIndexf( 8 );
// returns 6

@example
var n = fibonacciIndexf( NaN );
// returns NaN

@example
var n = fibonacciIndexf( 3.14 );
// returns NaN

@example
var n = fibonacciIndexf( -1 );
// returns NaN