notes from a conference with Jim Thomas and W. Kahan

[Bob Alverson]

* !cc CONDITIONALS IN C
* 
* Kahan proposes adding !< !<= !> !>= conditionals to C.  You could go further
* and add e.g. <? <=? >? >=?.  Among the four possible results of a comparison
* (equal, less, greater, unordered), 
* 
Why not make the !cc conditions without ? perform according to the
standard's NOT(cc)?  For example:

* < 	
* 	true on less
* 	false on equal or greater
* 	false with invalid exception on unordered

* <? or !>= 	
* 	true on less or unordered
* 	false on equal or greater

For !>=, the standard would have true with invalid exception on unordered

* 
* In other words, ordered comparisons involving NaNs with traditional
* operators are always false and raise an invalid exception.
* That protects old programs that weren't written with any thought of
* IEEE arithmetic.
* 
* Ordered comparisons involving NaNs with new operators might be true or false
* but never raise an exception.  Having control over exceptions is important
* if you want to efficiently code library functions without raising gratuitous
* exceptions.  Having language operators for a complete orthogonal set
* of conditionals is preferable from the point of view of efficiency
* to a set of external function calls.

The definition of !>= seems like a gratuitous deviation from the IEEE
standard.  Why make it redundant with <? when that conveys the message?
Hiding the ? by using the negation of the test seems like a step back
rather than an improvement.

Bob