COUPNUM should not return zero when settlement is in the last period

[myfonj]

Apparently what docs say ("rounded up to the nearest whole coupon") actually means that COUPNUM can never return 0.

=COUPNUM(DATE(2000;12;24);DATE(2000;12;24);4;0)
echo Financial::COUPNUM(date_create('2000-12-24'),date_create('2000-12-24'),4,0);
// settlement = maturity → Excel 2016 gives #NUMBER,  PHPOffice -1

=COUPNUM(DATE(2000;12;23);DATE(2000;12;24);4;0)
echo Financial::COUPNUM(date_create('2000-12-23'),date_create('2000-12-24'),4,0);
// settlement is one day before maturity → Excel 2016 gives 1, PHPOffice 0

=COUPNUM(DATE(2000;9;24);DATE(2000;12;24);4;0)
echo Financial::COUPNUM(date_create('2000-09-24'),date_create('2000-12-24'),4,0);
// settlement is on first coupon day before maturity → Excel 2016 gives 1, PHPOffice 0 

=COUPNUM(DATE(2000;9;23);DATE(2000;12;24);4;0)
echo Financial::COUPNUM(date_create('2000-09-23'),date_create('2000-12-24'),4,0);
// settlement is on day before first coupon day before maturity → Excel 2016 gives 2, PHPOffice 2 

Also, upon investigating it turned out current COUPNUM implementation somewhat lives in 365 year, or something.

PhpSpreadsheet/src/PhpSpreadsheet/Calculation/Financial.php

Lines 622 to 693 in ca56fd2

	/**
	* COUPNUM.
	*
	* Returns the number of coupons payable between the settlement date and maturity date,
	* rounded up to the nearest whole coupon.
	*
	* Excel Function:
	* COUPNUM(settlement,maturity,frequency[,basis])
	*
	* @category Financial Functions
	*
	* @param mixed $settlement The security's settlement date.
	* The security settlement date is the date after the issue
	* date when the security is traded to the buyer.
	* @param mixed $maturity The security's maturity date.
	* The maturity date is the date when the security expires.
	* @param mixed $frequency the number of coupon payments per year.
	* Valid frequency values are:
	* 1 Annual
	* 2 Semi-Annual
	* 4 Quarterly
	* If working in Gnumeric Mode, the following frequency options are
	* also available
	* 6 Bimonthly
	* 12 Monthly
	* @param int $basis The type of day count to use.
	* 0 or omitted US (NASD) 30/360
	* 1 Actual/actual
	* 2 Actual/360
	* 3 Actual/365
	* 4 European 30/360
	*
	* @return int|string
	*/
	public static function COUPNUM($settlement, $maturity, $frequency, $basis = 0)
	{
	$settlement = Functions::flattenSingleValue($settlement);
	$maturity = Functions::flattenSingleValue($maturity);
	$frequency = (int) Functions::flattenSingleValue($frequency);
	$basis = ($basis === null) ? 0 : (int) Functions::flattenSingleValue($basis);
	if (is_string($settlement = DateTime::getDateValue($settlement))) {
	return Functions::VALUE();
	}
	if (is_string($maturity = DateTime::getDateValue($maturity))) {
	return Functions::VALUE();
	}
	if (($settlement > $maturity) ||
	(!self::isValidFrequency($frequency)) ||
	(($basis < 0) || ($basis > 4))) {
	return Functions::NAN();
	}
	$settlement = self::couponFirstPeriodDate($settlement, $maturity, $frequency, true);
	$daysBetweenSettlementAndMaturity = DateTime::YEARFRAC($settlement, $maturity, $basis) * 365;
	switch ($frequency) {
	case 1: // annual payments
	return ceil($daysBetweenSettlementAndMaturity / 360);
	case 2: // half-yearly
	return ceil($daysBetweenSettlementAndMaturity / 180);
	case 4: // quarterly
	return ceil($daysBetweenSettlementAndMaturity / 90);
	case 6: // bimonthly
	return ceil($daysBetweenSettlementAndMaturity / 60);
	case 12: // monthly
	return ceil($daysBetweenSettlementAndMaturity / 30);
	}
	return Functions::VALUE();
	}

[MarkBaker]

Fixed in master

[myfonj]

Thanks for incorporating in #1068.