function logf( x, b ) {
	return float64ToFloat32( lnf( float64ToFloat32( x ) ) / lnf( float64ToFloat32( b ) ) );
}
Computes the base `b` logarithm of a single-precision floating-point number.

@param {NonNegativeNumber} x - input value
@param {NonNegativeNumber} b - base
@returns {number} logarithm (base `b`)

@example
var v = logf( 100.0, 10.0 );
// returns 2.0

@example
var v = logf( 16.0, 2.0 );
// returns 4.0

@example
var v = logf( 5.0, 1.0 );
// returns Infinity

@example
var v = logf( NaN, 2.0 );
// returns NaN

@example
var v = logf( 1.0, NaN );
// returns NaN

@example
var v = logf( -4.0, 2.0 );
// returns NaN

@example
var v = logf( 4.0, -2.0 );
// returns NaN