Datetime created from negative float timestamp is not monotonic (fraction part is added instead of substracted)

[mvorisek]

Description

The following code:

foreach ([0.4, 0, -0.4, -1, -1.4] as $ts) {
    $date = new DateTime('@' . $ts);
    print_r($date);
}

https://3v4l.org/EWpSj

Diff of current output vs expected:

 DateTime Object
 (
     [date] => 1970-01-01 00:00:00.400000
     [timezone_type] => 1
     [timezone] => +00:00
 )
 DateTime Object
 (
     [date] => 1970-01-01 00:00:00.000000
     [timezone_type] => 1
     [timezone] => +00:00
 )
 DateTime Object
 (
-    [date] => 1970-01-01 00:00:00.400000
+    [date] => 1969-12-31 23:59:59.600000
     [timezone_type] => 1
     [timezone] => +00:00
 )
 DateTime Object
 (
     [date] => 1969-12-31 23:59:59.000000
     [timezone_type] => 1
     [timezone] => +00:00
 )
 DateTime Object
 (
-    [date] => 1969-12-31 23:59:59.400000
+    [date] => 1969-12-31 23:59:58.600000
     [timezone_type] => 1
     [timezone] => +00:00
 )

PHP Version

present since PHP 8.0, should be fixed starting this version

it seems the issue is present only when TS is parsed, getTimestamp / format('u') seems correct across all PHP versions - https://3v4l.org/CjJLf

[damianwadley]

For the explanation: fractional timestamps are currently not supported when parsing, which means PHP handles inputs like @-1.4 as an absolute "@-1" (1970 minus 1s) followed by a relative ".4" (plus 0.4s).

[mvorisek]

For the explanation: fractional timestamps are currently not supported when parsing, which means PHP handles inputs like @-1.4 as an absolute "@-1" (1970 minus 1s) followed by a relative ".4" (plus 0.4s).

this is how it is parsed currently probably, however if unix timestamp is negative, the fractional part must be decremented as if the whole TS was a standard floating point number

https://3v4l.org/rKOAb shows the fractional part cannot be even used alone (eg. parsed with @ts token and the parsing must be fixed)

[iluuu1994]

I think it's fair to say that this a feature request as the docs do state that only whole numbers are supported.