07-328r2

To:          J3
From:        Stan Whitlock
Subject:     Interpretation request for IEEE_IS_NAN
Date:        2007 November 15


NUMBER: F03/0108
TITLE: Is IEEE_SUPPORT_NAN consistent with the other IEEE_SUPPORT
       functions
KEYWORDS: IEEE_SUPPORT_NAN, IEEE support functions
DEFECT TYPE: Clarification
STATUS: J3 consideration in progress


QUESTION:
The restriction of IEEE_IS_NAN requires that IEEE_SUPPORT_NAN returns
the value true.  The restrictions for the similar functions
IEEE_IS_{FINITE, NEGATIVE, and NORMAL} all require that
IEEE_SUPPORT_DATATYPE be true.  This is a much stronger restriction.

Should IEEE_SUPPORT_NAN also require that IEEE_SUPPORT_DATATYPE
return true?


ANSWER:

No.  The IEEE_IS_NAN restriction is weaker that requiring
IEEE_SUPPORT_DATATYPE but IEEE_IS_NAN is sufficient.
IEEE_SUPPORT_DATATYPE is used in IEEE_IS_FINITE, IEEE_IS_NEGATIVE,
and IEEE_IS_NORMAL because there are no IEEE_SUPPORT_* inquiry
functions to query support for finite, negative, or normal.
IEEE_SUPPORT_INF asks about infinities not finites and
IEEE_SUPPORT_DENORMAL only covers denormals and not the other
non-fintes (NaNs and Infinities).
EDITS:

None.

SUBMITTED BY: Dick Hendrickson

HISTORY: 07-328    m182  F03/0108 Submitted
         07-328r2  m182  Answer