Bug #79338 [Nab]: fmod() not calculating properly

Edit report at https://bugs.php.net/bug.php?id=79338&edit=1 ID: 79338 User updated by: ziggi at ziggi dot pl Reported by: ziggi at ziggi dot pl Summary: fmod() not calculating properly Status: Not a bug Type: Bug Package: *Math Functions Operating System: Windows PHP Version: 7.4.3 Block user comment: N Private report: N New Comment: OK, Not really good at all but obviously "obvious"... >> Get off my lawn. I do. Do not get upset so easy, man! Thank you for your time, anyway. Previous Comments: ------------------------------------------------------------------------ [2020-03-03 17:34:34] nikic@php.net > import math > print(math.fmod(75.6, 25.2)) 25.199999999999996 Surprising absolute nobody, Python returns the same result. Obviously. Get off my lawn. ------------------------------------------------------------------------ [2020-03-03 17:09:45] ziggi at ziggi dot pl Well, My conclusion: PHP: echo 2.0 * 2.0; outcome: 5.0 OMG! Why 2 * 2 is 5 in PHP??? Answer from PHP team: Because we use shitty C library with twisted precision so 2 * 2 is often 5. Enjoy or use Python. ------------------------------------------------------------------------ [2020-03-03 11:38:55] cmb@php.net Also note: <?php $num = 75.6; $denom = 25.2; $res = fmod($num, $denom); var_dump($res === $denom); // bool(false) ?> Further reading: <http://www.floating-point-gui.de/> ------------------------------------------------------------------------ [2020-03-03 11:35:11] nikic@php.net > cat test.c #include <math.h> #include <stdio.h> int main() { printf("%f\n", fmod(75.6, 25.2)); return 0; } > gcc test.c -lm > ./a.out 25.200000 ------------------------------------------------------------------------ [2020-03-03 11:20:41] ziggi at ziggi dot pl Description: ------------ --- From manual page: https://php.net/function.fmod --- I would say - simple answer provided by PHP team: "The value that you expect (0) is obtained using float precision. (In C) PHP uses double, and with this type fmod() returns 1.3." I completely pointless. This is not math! This is plain bullshit!!! Perl, MySQL, Python... you name it, all have no problems!!! Test script: --------------- echo fmod(75.6, 25.2); Expected result: ---------------- 0 Actual result: -------------- 25.2 ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=79338&edit=1