function daysInMonth(month, year)
{
  if (year == null) {
    var d = new Date();
    year = d.getFullYear();
  }
  if (month == 4 || month == 6 || month == 9 || month == 11) {
    return 30;
  } else if (month == 2) {
    if (year % 4 == 0) {
      return 29;
    } else {
      return 28;
    }
  } else {
    return 31;
  }
}

function sprintf() {
    function pad(str, len, chr, leftJustify) {
	var padding = (str.length >= len) ? '' : Array(1 + len - str.length >>> 0).join(chr);
	return leftJustify ? str + padding : padding + str;

    }

    function justify(value, prefix, leftJustify, minWidth, zeroPad) {
	var diff = minWidth - value.length;
	if (diff > 0) {
	    if (leftJustify || !zeroPad) {
		value = pad(value, minWidth, ' ', leftJustify);
	    } else {
		value = value.slice(0, prefix.length) + pad('', diff, '0', true) + value.slice(prefix.length);
	    }
	}
	return value;
    }

    function formatBaseX(value, base, prefix, leftJustify, minWidth, precision, zeroPad) {
	// Note: casts negative numbers to positive ones
	var number = value >>> 0;
	prefix = prefix && number && {'2': '0b', '8': '0', '16': '0x'}[base] || '';
	value = prefix + pad(number.toString(base), precision || 0, '0', false);
	return justify(value, prefix, leftJustify, minWidth, zeroPad);
    }

    function formatString(value, leftJustify, minWidth, precision, zeroPad) {
	if (precision != null) {
	    value = value.slice(0, precision);
	}
	return justify(value, '', leftJustify, minWidth, zeroPad);
    }

    var a = arguments, i = 0, format = a[i++];
    return format.replace(sprintf.regex, function(substring, valueIndex, flags, minWidth, _, precision, type) {
	    if (substring == '%%') return '%';

	    // parse flags
	    var leftJustify = false, positivePrefix = '', zeroPad = false, prefixBaseX = false;
	    for (var j = 0; flags && j < flags.length; j++) switch (flags.charAt(j)) {
		case ' ': positivePrefix = ' '; break;
		case '+': positivePrefix = '+'; break;
		case '-': leftJustify = true; break;
		case '0': zeroPad = true; break;
		case '#': prefixBaseX = true; break;
	    }

	    // parameters may be null, undefined, empty-string or real valued
	    // we want to ignore null, undefined and empty-string values

	    if (!minWidth) {
		minWidth = 0;
	    } else if (minWidth == '*') {
		minWidth = +a[i++];
	    } else if (minWidth.charAt(0) == '*') {
		minWidth = +a[minWidth.slice(1, -1)];
	    } else {
		minWidth = +minWidth;
	    }

	    // Note: undocumented perl feature:
	    if (minWidth < 0) {
		minWidth = -minWidth;
		leftJustify = true;
	    }

	    if (!isFinite(minWidth)) {
		throw new Error('sprintf: (minimum-)width must be finite');
	    }

	    if (!precision) {
		precision = 'fFeE'.indexOf(type) > -1 ? 6 : (type == 'd') ? 0 : void(0);
	    } else if (precision == '*') {
		precision = +a[i++];
	    } else if (precision.charAt(0) == '*') {
		precision = +a[precision.slice(1, -1)];
	    } else {
		precision = +precision;
	    }

	    // grab value using valueIndex if required?
	    var value = valueIndex ? a[valueIndex.slice(0, -1)] : a[i++];

	    switch (type) {
		case 's': return formatString(String(value), leftJustify, minWidth, precision, zeroPad);
		case 'c': return formatString(String.fromCharCode(+value), leftJustify, minWidth, precision, zeroPad);
		case 'b': return formatBaseX(value, 2, prefixBaseX, leftJustify, minWidth, precision, zeroPad);
		case 'o': return formatBaseX(value, 8, prefixBaseX, leftJustify, minWidth, precision, zeroPad);
		case 'x': return formatBaseX(value, 16, prefixBaseX, leftJustify, minWidth, precision, zeroPad);
		case 'X': return formatBaseX(value, 16, prefixBaseX, leftJustify, minWidth, precision, zeroPad).toUpperCase();
		case 'u': return formatBaseX(value, 10, prefixBaseX, leftJustify, minWidth, precision, zeroPad);
		case 'i':
		case 'd': {
			      var number = parseInt(+value);
			      var prefix = number < 0 ? '-' : positivePrefix;
			      value = prefix + pad(String(Math.abs(number)), precision, '0', false);
			      return justify(value, prefix, leftJustify, minWidth, zeroPad);
			  }
		case 'e':
		case 'E':
		case 'f':
		case 'F':
		case 'g':
		case 'G':
		          {
			      var number = +value;
			      var prefix = number < 0 ? '-' : positivePrefix;
			      var method = ['toExponential', 'toFixed', 'toPrecision']['efg'.indexOf(type.toLowerCase())];
			      var textTransform = ['toString', 'toUpperCase']['eEfFgG'.indexOf(type) % 2];
			      value = prefix + Math.abs(number)[method](precision);
			      return justify(value, prefix, leftJustify, minWidth, zeroPad)[textTransform]();
			  }
		default: return substring;
	    }
		    });
}
sprintf.regex = /%%|%(\d+\$)?([-+#0 ]*)(\*\d+\$|\*|\d+)?(\.(\*\d+\$|\*|\d+))?([scboxXuidfegEG])/g;