Formal comment #167 (defect)

floor, ceiling, truncate, and round are unnecessarily over-specified on infinities and NaNs
Reported by: 	Brad Lucier
Version:	5.92

On page 44 of the main body of the report, the description of floor,
ceiling, truncate, and round contains the text

> Although infinities and NaNs are not integers, these pro-
> cedures return an infinity when given an infinity as an ar-
> gument, and a NaN when given a NaN.

The same text appears in the "Standard Libraries" document when
describing the flonum-specific versions of the same functions, namely
flfloor, flceiling, fltruncate, and flround.

I consider the fact that the flonum versions of these operations are
designed to operate in this way to be an optimization issue, in that
common hardware implementations of IEEE 754 arithmetic act in this
way, just as both R5.92RS flsqrt *may* return a NaN and IEEE 754 sqrt
*is defined* to return NaN when given the argument "-1.". In R*RS,
however, "(sqrt -1)" is expected to do "the right thing" and return a
complex imaginary unit if complex numbers are available.

I have argued in the past, and will continue to do so, that the
generic arithmetic versions of these functions should return only
integers, and that, in a "safe" environment (I know, I know, the
existence of such things are no longer mandated) passing an infinity
or a NaN to these four functions should throw an exception. I believe
that implementations should be given the freedom to do exactly
that. If people want the IEEE 754 behavior of these functions, they
can call the fl* versions of these functions.

So I suggest that the current wording should be kept in the
specification of the fl* versions of these functions, and be removed
from the main body of the report.

Brad


RESPONSE:

The advantage of the proposal is conceptual: the floor,
ceiling, truncate, and round procedures would always
return an integer result.

The main disadvantage of this proposal is that it would
introduce exceptions (pun intended) to the simple rule
that the floor, ceiling, truncate, and round procedures
behave the same as the the flfloor, flceiling, fltruncate,
and flround procedures on flonum arguments.  That doesn't
matter much.

A majority of the editors voted not to adopt the formal 
comment's proposal.