Bug 62644 - math addition and subtraction errors
Summary: math addition and subtraction errors
Alias: None
Product: Red Hat Linux
Classification: Retired
Component: gnome-utils (Show other bugs)
(Show other bugs)
Version: 7.2
Hardware: i386 Linux
Target Milestone: ---
Assignee: Havoc Pennington
QA Contact: Brian Brock
Depends On:
TreeView+ depends on / blocked
Reported: 2002-04-03 18:14 UTC by Craig
Modified: 2008-08-01 16:22 UTC (History)
0 users

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
Last Closed: 2002-04-10 15:00:04 UTC
Type: ---
Regression: ---
Mount Type: ---
Documentation: ---
Verified Versions:
Category: ---
oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

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Description Craig 2002-04-03 18:14:20 UTC
From Bugzilla Helper:
User-Agent: Mozilla/5.0 (X11; U; Linux i586; en-US; rv:0.9.7) Gecko/20011226

Description of problem:
Using perl, php or even the gnome calculator, adding 39.9+19.95=59.85
subtracting 59.85 should = 0 but does not. (very small number -7.10543e-15)

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
1.in X windows (I used gnome calculator) add 39.9 to 19.95 and subtract   
the sum (59.85) which should equal 0

2. write a perl script to add and subtract these numbers
3. write a php script to add and subtract these numbers

Actual Results:  You get output of -7.10543e-15 instead of 0

Expected Results:  You should get 0

Additional info:

We've countered this problem in scripting by using an if < than 0 statement.
Linux rocks, but it should add and subtract right. (Micorsoft products do (yuk)

Comment 1 Trond Eivind Glomsrxd 2002-04-10 14:59:57 UTC
Floating point math isn't exact - you can't represent an infinite range (R - all
real numbers) in a finite space of 2^(precision) combinations. Thus, don't count
on having a specific number when you have done a series of numerical
calculations. This is especially a problem with 0, as if it was 1+1e-20, the
last part would be truncated when displayed.

Comment 2 Havoc Pennington 2002-04-10 15:03:18 UTC
In perl/php this is entirely normal and expected, that's how floating point
calculations work, they have limited precision.

The calculator app should work around it though, bug filed upstream here:

Closing on Red Hat level.

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