protected static function adapt($delta, $numpoints, $firsttime) {
#	function adapt(delta,numpoints,firsttime):
#		if firsttime then let delta = delta div damp
		if ($firsttime) {
			$delta = floor($delta / self::BOOTSTRAP_DAMP);
		}
#		else let delta = delta div 2
		else {
			$delta = floor($delta / 2);
		}
#		let delta = delta + (delta div numpoints)
		$delta += floor($delta / $numpoints);
#		let k = 0
		$k = 0;
#		while delta > ((base - tmin) * tmax) div 2 do begin
		$max = floor(((self::BOOTSTRAP_BASE - self::BOOTSTRAP_TMIN) * self::BOOTSTRAP_TMAX) / 2);
		while ($delta > $max) {
#			let delta = delta div (base - tmin)
			$delta = floor($delta / (self::BOOTSTRAP_BASE - self::BOOTSTRAP_TMIN));
#			let k = k + base
			$k += self::BOOTSTRAP_BASE;
#		end
		}
#		return k + (((base - tmin + 1) * delta) div (delta + skew))
		return $k + floor(((self::BOOTSTRAP_BASE - self::BOOTSTRAP_TMIN + 1) * $delta) / ($delta + self::BOOTSTRAP_SKEW));
	}