Proper definition of Modelica.Constants.{eps,small}

[modelica-trac-importer]

Reported by hansolsson on 6 Sep 2016 13:33 UTC
The values are now given in ModelicaServices - but my problem isn't the values, but the definitions.

In Modelica.Constants it says:
final constant Real eps "Biggest number such that 1.0 + eps = 1.0";
final constant Real small "Smallest number such that small and -small are representable on the machine";
final constant Real inf "Biggest Real number such that inf and -inf are representable on the machine";
--
The name "inf" not well-chosen - but apart from that according to the definitions we have on an normal intel-based computer:
inf=1.7976931348623157E+308
eps =1.1102230246251565E-016
small=4.94065645841247E-324 (denormalized number)

Compare this with the C-standard:
#define DBL_EPSILON 2.2204460492503131e-016
/* smallest such that 1.0+DBL_EPSILON != 1.0 */

#define DBL_MIN 2.2250738585072014e-308
/* min positive value */

(The actual C11-standard makes it clear that DBL_MIN is a normalized floating point number.)

The previous values of eps and small were conservative estimates such that 1+eps>1 and 1/small was defined. The impact of using eps such that 1+eps=1 or denormalized small is unknown.

I would prefer to map this to DBL_MAX, DBL_EPS and DBL_MIN - and thus adapt the definitions so that this is true.

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Migrated-From: https://trac.modelica.org/Modelica/ticket/2056

[modelica-trac-importer]

Comment by hansolsson on 6 Sep 2016 13:40 UTC
In C11:
DBL_EPS is:
the difference between 1 and the least value greater than 1 that is representable in the given floating point type

DBL_MIN is:
minimum normalized positive floating-point number

DBL_MAX is:
maximum representable finite floating-point number !

[AHaumer]

see #3081 for further remarks