Bug #81601 [Com]: float - (int) float is sometimes bigger than 1

Edit report at https://bugs.php.net/bug.php?id=81601&edit=1 ID: 81601 Comment by: dktapps at pmmp dot io Reported by: dktapps at pmmp dot io Summary: float - (int) float is sometimes bigger than 1 Status: Open Type: Bug Package: Math related Operating System: Linux PHP Version: 8.0.12 Block user comment: N Private report: N New Comment: I should clarify, this is definitely NOT a bug in JIT because I've seen this issue in 7.2, 7.3 and 7.4 historically as well. I also considered the possibility that -ffast-math may be responsible, but I was unable to reproduce the problem even with -ffast-math. All tests were done on x86_64. Previous Comments: ------------------------------------------------------------------------ [2021-11-08 19:39:38] dktapps at pmmp dot io Description: ------------ I've seen this issue recur many times over the last few years, but never figured out exactly what causes it. This code: https://github.com/pmmp/PocketMine-MP/blob/3dae87373154ad52ff6c27874f3fd93c9845a8af/src/pocketmine/entity/Human.php#L396 is intended to take a float and split it into its whole-number part (the first argument) and its fractional part (the second argument). However, sometimes I see crashes like these show in my telemetry: Value 1.0323429203787 is outside the range 0 - 1 with a trace like this: #1 pmsrc/src/pocketmine/entity/Human(396): pocketmine\entity\Human->setXpAndProgress(integer 9, double 1.0323429203787) #2 pmsrc/src/pocketmine/entity/Human(409): pocketmine\entity\Human->setCurrentTotalXp(integer 158) To the best of my understanding, this should be impossible. For context, passing 158 into setCurrentTotalXp() causes $newLevel to become float(9.922847983320086), which, when run through the offending code on **my** machine, yields this result: (int) $newLevel = int(9) $newLevel - (int) $newLevel = float(0.9228479833200858) which looks correct. I have no idea what causes this problem and have never been able to reproduce it firsthand, but such issues have appeared so frequently and across several PHP versions that I believe this is a bug in PHP itself. Expected result: ---------------- float - (int) float should never be larger than 1. Actual result: -------------- float - (int) float is sometimes slightly larger than 1. ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=81601&edit=1