Experimental Physics and
Industrial Control System

Benjamin Franksen <[email protected]> · Fri, 08 Oct 1999 20:49:15 +0200

Sue Witherspoon wrote:
> 
> The problem is in the epics alarm subroutine:
>   (snipit from an ai record)
> ...
> The comparison between a double and a float is okay as long as the precision of
> the comparison is not very large. For instance
> 
>  if val = 125303.000 and hihi = 125303.001 the above comparision
>  would give you an alarm.
> 
> On the surface the solution would be to change the type of hihi to
> be double but on further inspection the ascii file for this record
> says that the field is DBF_FLOAT? Does this imply that the
> size of the record must also change?

Yes, a DBF_FLOAT is compiled (by dbRecordtypeH) to 'float' and
DBF_DOUBLE to 'double'.

I never quite understood why so many of the ai and ao record's fields
are float instead of double. Another example where this leads to wrong
results are the AOFF and ASLO fields. You cannot represent a 32 bit
integer (RVAL) with a float without loosing precision.

I'd propose to make all analog fields doubles.

Ben

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System