Motion 24.03_yes
My vote on Motion 24.03 is: Yes.
I note that the mandate applies to the run-time environment, and
not necessarily to the hardware (as Dan Zuras appears to imply).
The point is that IF the hardware were to support explicit directed-rounding
arithmetic efficiently, there should be a UNIFORM way for the programmer to
exploit this. Otherwise we'll either get suboptimal programs, or an #ifdef
zoo to handle the subset of platforms that the programmer happens to know
well enough to exploit uderlying capabilities.
I do admit the possibility that optimizing compilers would be able to
extract the programmer's intent in low_bound(interval(a)+interval(b))
and discard the computation leading to the unused high-bound on platforms
where that would be a separate computation. Perhaps Ian McIntosh could
enlighten us on how likely that might be. (The standard could include an
informative note that this could be one way to address the issue -- but
in that case the platform could easily encapsulate such idioms in macros
that satisfy Motion 24.03 directly.)
In other words, I still prefer a solution where the programmer can state
intent directly, instead of relying on side-effects of circumlocutions.
Michel.
---Sent: 2011-07-06 19:49:21 UTC