trace(checkValidValue(3));
// 2 と出力

function checkValidValue(val:Number):Number {
	var stepS:Number = 2;
	var minVal:Number = 1;
	var maxVal:Number = 99;
	var initDiv:Number = val / stepS;
	var roundD:Number = Math.floor(initDiv);
	if (val > minVal and val < maxVal) {
		if (initDiv - roundD == 0) {
			return val;
		} else {
			var tmpV:Number = Math.floor(val / stepS);
			var stepDownV:Number = tmpV * stepS;
			if ((val - stepDownV >= stepS / 2 && maxVal >= stepDownV + stepS && minVal <= stepDownV - stepS)
				|| (val + stepS == maxVal && maxVal - stepDownV - stepS > 0.00000000000001)) {
				stepDownV += stepS;
			}
			return stepDownV;
		}
	} else {
		if (val >= maxVal) {
				return maxVal;
		} else {
			return minVal;
		}
	}
}

import mx.controls.NumericStepper;

my_nstep.minimum = 1;
my_nstep.maximum = 99;
my_nstep.stepSize = 1;
my_nstep.value = my_nstep.minimum;

function dataIsInvalid(evt) {
	if (evt.property == "text") {
		status.text = evt.messages;
	}
}
function dataIsValid(evt) {
	if (evt.property == "text") {
		status.text = "OK";
	}
}
textLabel.addEventListener("valid", dataIsValid);
textLabel.addEventListener("invalid", dataIsInvalid);