Public Comment Number PC-UK0144 ISO/IEC CD 9899 (SC22N2620) Public Comment =========================================== Date: 1998-02-25 Author: N.M Maclaren Author Affiliation: Self Postal Address: University of Cambridge, Computer Laboratory, New Museums Site, Pembroke Street, Cambridge CB3 3QG, United Kingdom E-mail Address: Telephone Number: +44 1223 334761 Fax Number: +44 1223 334679 Number of individual comments: 1 Comment 1. Category: Normative change to existing feature retaining the original intent Committee Draft subsection: 7.7.3.2 Title: Serious confusion in the signbit macro Detailed description: The wording of this is seriously flawed. It says that it returns the sign of a number, but is clearly intended to test the sign bit, and these are NOT equivalent. IEEE 754 states explicitly that it does not use the sign bit of NaNs as a sign bit, and all VAX NaNs have sign bit zero (the equivalents with sign bit one are invalid numbers and not NaNs.) And there is nowhere else in C9X that requires the sign of a floating-point number to be held as a bit - surely people have not yet forgotten ones' and twos' complement floating point? I suggest replacing paragraphs 2 and 3 and footnote 175 by: 2a For valid non-zero values (including infinities but not NaNs), the signbit macro returns nonzero if and only if the sign of its argument is negative. 2b For zeroes and NaNs when __STD_IEC_559__ is defined, the signbit macro returns nonzero if and only the sign bit of the value is set. 2c For zeroes and NaNs when __STD_IEC_559__ is not defined, the signbit macro returns nonzero for an implementation-defined set of values and zero otherwise.