function floorb( x, n, b ) {
	return addon( x, n, b );
}
Rounds a numeric value to the nearest multiple of \\(b^n\\) toward negative infinity.

@private
@param {number} x - input value
@param {integer} n - integer power
@param {PositiveInteger} b - base
@returns {number} rounded value

@example
// Round a value to 4 decimal places:
var v = floorb( 3.141592653589793, -4, 10 );
// returns 3.1415

@example
// If n = 0 or b = 1, `floorb` behaves like `floor`:
var v = floorb( 3.141592653589793, 0, 2 );
// returns 3.0

@example
// Round a value to the nearest multiple of two toward negative infinity:
var v = floorb( 5.0, 1, 2 );
// returns 4.0