On Mon, 7 Mar 2011 10:03:37 -0500 "Stewart, Robert" <Robert.Stewart@sig.com> wrote:
[...] For that matter, pretty much everything in the library is implemented in terms of addition, subtraction, multiplication, division, modulus, comparisons, and the occasional bit-manipulation function or is_odd/is_even. All of which are in the public interface. Lower-level access might occasionally allow for a faster implementation, but it's almost never required. (I'd go so far as to say never, but there's an exception to every rule.)
That is, of course, very likely. The hidden part of the question is whether such an algorithm can be implemented efficiently without needing access to the internals.
That depends on the algorithm. There are a few (random_by_size springs to mind) that require access to the internals for maximum efficiency. However, most algorithms have no need for that. Even relatively complex ones, like powmod with the Montgomery reduction algorithm, can be efficiently expressed entirely through the current public interface.
Note, this is the same thing being asked related to expression templates. The idea there is to reduce a non-trivial sequence of operations to some provided public function that does a combination of operations in one call taking advantage of the internals. IOW, if you provide a function that does "add two numbers and multiply the result by a third" implemented in some manner that is more efficient than the naive sequence, then you can use ETs to recognize that pattern (product of a sum and a third value) and call the special function rather than apply the naive sequence of operations. [...]
Yes, I'm starting to realize that. I'm not sure that it will be of much use to most people, but it could be indispensable to a few. I'm pretty sure it can be added without changing the existing public interface or breaking client code that uses it, but I'm still pondering the possibilities. -- Chad Nelson Oak Circle Software, Inc. * * *