Fixed Point Subtypes inheriting Small 87-02-10 AI-00521/00 1
!standard 03.05.09 (14) 87-02-10 AI-00521/00
!class study 87-02-10 (provisional classification)
!status received 87-02-10
!topic Fixed Point Subtypes inheriting Small
!summary 87-02-10
!question 87-02-10
!recommendation 87-02-10
!wording 87-02-10
!discussion 87-02-10
!appendix 87-02-10
*****************************************************************************
!section 03.05.09 (14) Terry Froggatt 86-12-05 83-00884
!version 1983
!topic Fixed Point Subtypes inheriting Small
3.5.9 (14) states, and 3.5.9 (16) clarifies, that a fixed point subtype S
of a fixed point type T, inherits the Small of T if and only if that Small
was specified by a length clause.
However, I imagine that most fixed point types will have a small length
clause to ensure that Small is Delta rather than a power of 2. I cannot
see small length clauses being used to produce a much smaller small than
the delta, since this this can be achieved by using a smaller delta.
A subtype of T which inherits T's small can always be obtained by
using a range constraint rather than a fixed-point constraint;
so if a fixed-point constraint is given it should be honoured.
Thus, the Small of S should be the largest power of 2 times the Small
of T that is not more than the Delta of the fixed-point constraint;
regardless of whether T's Small was specified or defaulted.