[R] Was Logical inconsistency - algorithm portability

John C Nash
Tue, 09 Dec 2008 17:36:55 -0000

The "logical inconsistency" thread has wandered a bit and discussion
now veers towards portability of algorithms. On that subject, I have off-list
been sharing ideas about the existence of functions to ensure optimizing
compilers do not corrupt logical tests in numerical methods. Apparently the
"volatile" adjective may have a role here (I am generally a
"visiting programmer" in C, doing just enough to get things to work,
and cribbing other folks' code).

One need is for a function that ensures the stored representation of numbers is
returned, call it "STORED", so that one can test if STORED(x) ==
STORED(y). Various hacks can do this. One time we used an array of length 2. But
hacks are generally ugly and vulnerable to updates in compilers, so a properly
written and documented function would be helpful. And, of course, may already
exist.

As this is not a short-term help request but a long term need, I suggest
contacting me off list about this subject.

Cheers,JN