php.net |  support |  documentation |  report a bug |  advanced search |  search howto |  statistics |  random bug |  login

go to bug id or search bugs for

Bug #50824 modulus (mod) returns wrong value
Submitted: 2010-01-22 14:46 UTC Modified: 2010-01-22 21:49 UTC
From: jancha at trave dot lv Assigned:
Status: Not a bug Package: Math related
PHP Version: 5.2.12 OS: Gentoo
Private report: No CVE-ID: None
View Developer Edit
Welcome back! If you're the original bug submitter, here's where you can edit the bug or add additional notes.
If you forgot your password, you can retrieve your password here.
Password:
Status:
Package:
Bug Type:
Summary:
From: jancha at trave dot lv
New email:
PHP Version: OS:

 

 [2010-01-22 14:46 UTC] jancha at trave dot lv 
Description:
------------
We came accorss following  case:

<?php echo 72.6 * 100 % 100;

You would expect: 60
But you get: 59

We did further analysis and got following results:
[OK] 72.0:0
[FAIL] 72.1:9 
[OK] 72.2:20 
[OK] 72.3:30
[OK] 72.4:40
[OK] 72.5:50
[FAIL] 72.6:59
[OK] 72.7:70
[OK] 72.8:80
[OK] 72.9:90

That makes us think that bug happens, if last digit is either 1 or 6. Also, according to manual, operands of modulus are converted to integers by stripping decimal part away - in our case that is not reason, as 72.6 * 100 = 7260 (float). And conversion to int should result with 7260.

Reproduce code:
---------------
<?php echo 72.6 * 100 % 100;

Expected result:
----------------
60

Actual result:
--------------
59

Patches

Pull Requests

History

AllCommentsChangesGit/SVN commitsRelated reports
 [2010-01-22 15:07 UTC] rasmus@php.net 
Floating point values have a limited precision. Hence a value might 
not have the same string representation after any processing. That also
includes writing a floating point value in your script and directly 
printing it without any mathematical operations.

If you would like to know more about "floats" and what IEEE
754 is, read this:
http://docs.sun.com/source/806-3568/ncg_goldberg.html
 
Thank you for your interest in PHP.

72.6 * 100 is not exactly 7260
 [2010-01-22 21:49 UTC] jancha at trave dot lv 
temporary patch would be:

<?php echo round(72.6 * 100) % 100;

That would indeed result with: 60
 
PHP Copyright © 2001-2025 The PHP Group
All rights reserved. 		Last updated: Wed Jan 15 08:01:29 2025 UTC