\DateInterval 1.5s added to DateTimeInterface is rounded down since PHP 8.1.0

[norberttech]

Description

The following code:

<?php

$start = new \DateTimeImmutable("2020-01-01 00:00:00 UTC");

$oneAndHalfSec = new \DateInterval("PT1S");
$oneAndHalfSec->f = 0.5;

$t1 = $start->add($oneAndHalfSec);
$t2 = $t1->add($oneAndHalfSec);
$t3 = $t2->add($oneAndHalfSec);
$t4 = $t3->add($oneAndHalfSec);

var_dump($start->getTimestamp());
var_dump($t1->getTimestamp());
var_dump($t2->getTimestamp());
var_dump($t3->getTimestamp());
var_dump($t4->getTimestamp());

Resulted in this output in PHP 8.1.0 - 8.1.8:

int(1577836800)
int(1577836801)
int(1577836802)
int(1577836803)
int(1577836804)

But I expected this output instead, like in PHP 7.4.0 - 7.4.30, 8.0.1 - 8.0.21:

int(1577836800)
int(1577836801)
int(1577836803)
int(1577836804)
int(1577836806)

PHP Version

8.1.8

Operating System

No response

[cmb69]

Confirmed: https://3v4l.org/jV4V0. The issue is similar to #8964, but this time it is about timelib_add_wall() instead of timelib_sub_wall(). Particularly:

php-src/ext/date/lib/interval.c

Lines 367 to 371 in eff9aed

	t->us += interval->us * bias;
	if (bias == -1 && interval->us > 0) {
	t->sse--;
	}
	timelib_do_normalize(t);

The addition in line 367 yields the correct result for the second addition (s=2, us=1000000), and the following timelib_do_normalize() correctly normalizes (s=3, us=0), but sse is not properly updated.

[derickr]

This is now fixed through #9176

[norberttech]

Thanks!