Experimental Physics and
Industrial Control System

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<== Date ==>		<== Thread ==>

Subject:	ABS() in calc record
From:	"Laznovsky Michael (PSI)" <[email protected]>
To:	"[email protected]" <[email protected]>, "[email protected]" <[email protected]>
Date:	Sat, 21 May 2016 10:43:54 +0000

Hello- to the keepers of the Sacred Source Code, in the course of developing some

displays I noticed that a PV which should never be < 0 had a persistent flickering minus

sign (-0.000)... the cause was traced to the implentation of ABS in the calc record, ie:

case ABS_VAL:

if (*ptop < 0.0) *ptop = - *ptop;

break;

In my case, the CALC is "ABS(A*B)", and e.g. A=0 and B<0 results in ABS(-0), which does

not satisfy the if() in the code because -0 is NOT less than zero, so the sign is not flipped

back to positive.

Using fabs() instead fixes it (and probably also saves a branch).

cheers,

Mike

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Replies:: RE: ABS() in calc record Laznovsky Michael (PSI); Re: ABS() in calc record Johnson, Andrew N.

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ANJ, 15 Jul 2016