Experimental Physics and
Industrial Control System

Marty Kraimer <[email protected]> · Fri, 11 Jun 2004 07:01:11 -0500

IOC database access converts DBF_FLOAT to DBR_STRING by calling
cvtFloatToString.

Similarly DBF_DOUBLE is converted to DBR_STRING by calling
cvtDoubleToString.

Both accept precision as an argument.
In 3.14 they are in <base>/src/libCom/cvtFast/cvtFast.c
For moderate size values precision means number of decimal places. See
the code for how it handles large numbers or precision > 8.
Early versions of vxWorks had a very slow implementation of %g format
conversion. It could only do about 100 conversions per second on a
68020. Thus cvtFast.c was created.
Note that cvtFast has a number of usefull converrsion routines:

 cvtFloatToString(float value, char *pstring, unsigned short
precision);

cvtDoubleToString(double value, char *pstring, unsigned short
precision);

cvtFloatToExpString(float value, char *pstring, unsigned short
precision);

cvtDoubleToExpString(double value, char *pstring, unsigned short
precision);

cvtFloatToCompactString(float value, char *pstring, unsigned
short precision);

cvtDoubleToCompactString(double value, char *pstring, unsigned
short precision);

cvtCharToString(signed char value, char *pstring);

cvtUcharToString(unsigned char value, char *pstring);

cvtShortToString(short value, char *pstring);

cvtUshortToString(unsigned short value, char *pstring);

cvtLongToString(epicsInt32 value, char *pstring);

cvtUlongToString(epicsUInt32 value, char *pstring);

cvtLongToHexString(epicsInt32 value, char *pstring);

cvtLongToOctalString(epicsInt32 value, char *pstring);

Dirk Zimoch wrote:
Hi all,
we all know the PREC field of many records. Unforunately, its purpose
is not documented very precisely. The Application Developer's Guide
says in chapter 3.5.1 (EPICS Overview - Channel Access - Client
Services):
"In addition to requesting process variable values, any combination of
the following additional information may be requested:

[...]

* Precision: Precision with which to display floating point numbers."
In the Record Reference Manual, one can read e.g. in the ai chapter:
"The PREC field determines the floating point precision with which to
display VAL."
But what does this exactly mean? I think, the most intuitive sense is
to format the value like "%.<PREC>f". At least this is the default
behaviour of medm when using a text monitor. But why not like
"%.<PREC>g" or "%.<PREC>e"? And why does neither caget nor camonitor
honor PREC? And what about negative PREC values?
I suggest the following:
PREC >= 0 means to format the value like printf("%.*f",PREC,VAL);
PREC < 0  means to format the value like printf("%.*e",-PREC,VAL);
All tools including caget and camonitor should honor PREC.
Any comments?
Dirk

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System