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

go to bug id or search bugs for

Bug #66737 5.5 wrongly rounded to 5
Submitted: 2014-02-18 20:29 UTC Modified: 2014-02-18 20:55 UTC
From: mail at daniel-berlin dot de Assigned:
Status: Not a bug Package: Math related
PHP Version: 5.5.9 OS: Linux
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: mail at daniel-berlin dot de
New email:
PHP Version: OS:

 

 [2014-02-18 20:29 UTC] mail at daniel-berlin dot de 
Description:
------------
5.5 is wrongly rounded to 5 (even with PHP_ROUND_HALF_UP)

Test script:
---------------
<?php

$n = 2.2459431618637;

echo "Expected 5.5 / is " .
     round(pow(1024, $n - floor($n)), 2, PHP_ROUND_HALF_UP) . "\n";

echo "Expected 5.5 / is " .
     round(pow(1024, $n - floor($n)), 1, PHP_ROUND_HALF_UP) . "\n";

echo "Expected 6   / is " .
     round(pow(1024, $n - floor($n)), 0, PHP_ROUND_HALF_UP) . "\n";

echo "Expected 5.50 / is " . number_format(pow(1024, $n - floor($n)), 2) . "\n";
echo "Expected 5.5  / is " . number_format(pow(1024, $n - floor($n)), 1) . "\n";
echo "Expected 6    / is " . number_format(pow(1024, $n - floor($n)), 0) . "\n";


Expected result:
----------------
See output (line 3 and 6 are wrong):

Expected 5.5 / is 5.5
Expected 5.5 / is 5.5
Expected 6   / is 5
Expected 5.50 / is 5.50
Expected 5.5  / is 5.5
Expected 6    / is 5


Actual result:
--------------
See expected result.

Patches

Pull Requests

History

AllCommentsChangesGit/SVN commitsRelated reports
 [2014-02-18 20:30 UTC] mail at daniel-berlin dot de 
Reproducible with PHP 5.5.4 (cli)
 [2014-02-18 20:55 UTC] requinix@php.net
-Status: Open +Status: Not a bug
 [2014-02-18 20:55 UTC] requinix@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://www.floating-point-gui.de/

Thank you for your interest in PHP.

On my system, pow(1024, $n - floor($n)) == 5.4999999999989.
 
PHP Copyright © 2001-2024 The PHP Group
All rights reserved. 		Last updated: Sun Dec 22 04:01:29 2024 UTC