Experimental Physics and
Industrial Control System

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 <2016> 2017 2018 2019 2020 2021 2022 2023 2024	Index	1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 <2016> 2017 2018 2019 2020 2021 2022 2023 2024
<== Date ==>		<== Thread ==>

Subject:	RE: FLOOR function in EPICS CALC error
From:	"Mooney, Tim M." <[email protected]>
To:	"[email protected]" <[email protected]>, "[email protected]" <[email protected]>
Date:	Fri, 11 Nov 2016 20:23:03 +0000

I just tried this in python, and I get the same result.
>>> math.floor((6.1-.2)/.01)
589.0

Here's why:

>>> d=((6.1-.2)/.01)
>>> print("%.18f"%d)
589.999999999999886313

Tim Mooney ([email protected]) (630)252-5417
Beamline Controls Group (www.aps.anl.gov)
Advanced Photon Source, Argonne National Lab

From: [email protected] [[email protected]] on behalf of [email protected] [[email protected]]
Sent: Friday, November 11, 2016 2:08 PM
To: [email protected]
Subject: FLOOR function in EPICS CALC error

Hi,

I am seeing what I think may be a rounding error in the FLOOR function and I was wondering if others had seen this. I replaced the variables in my code with actual values to reproduce the problem. I am using EPICS R3.14.12.5 with Scientific Linux 7. I also tried it with the same version of EPICS running on Linux Mint

In Calc records, just using an empty Calc record and putting the values in by hand:

record(calc,"DLY:FSTEP")

{

field(CALC,"6.1-0.2/0.01")

}

6.1-0.2/0.01 gives 590 as it should

However:

FLOOR((6.1-0.2)/0.01)

Gives me 589

If I write it as follows:

FLOOR((6.1-0.2)*(1/0.01))

I again get 590 (as it should be)