function truncb( x, n, b ) {
	var y;
	var s;
	if (
		isnan( x ) ||
		isnan( n ) ||
		isnan( b ) ||
		b <= 0 ||
		isInfinite( n ) ||
		isInfinite( b )
	) {
		return NaN;
	}
	if ( isInfinite( x ) || x === 0.0 ) {
		return x;
	}
	if ( b === 10 ) {
		return truncn( x, n );
	}
	if ( n === 0 || b === 1 ) {
		return trunc( x );
	}
	s = pow( b, -n );

	// Check for overflow:
	if ( isInfinite( s ) ) {
		return x;
	}
	y = trunc( x*s ) / s;

	// Check for overflow:
	if ( isInfinite( y ) ) {
		return x;
	}
	return y;
}
Rounds a numeric value to the nearest multiple of \\(b^n\\) toward zero.

@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 = truncb( 3.141592653589793, -4, 10 );
// returns 3.1415

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

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