dlw_gcd review comments.

From: Hubert HOLIN (Hubert.Holin_at_[hidden])
Date: 2001-09-26 16:40:08

Paris (U.E.), le 26/09/2001 (just in time...).

        Hi

                I have only had the time to look at the gcd/lcm library.

                I recommend Boost accept that library. It is useful and 
correct (including the special cases).

                A few comments are in order, however:

1) use of the "%" operator might lead to portability problems, as noted 
by another; the best fix would probably be to move to positive numbers 
sooner.

2) no way (that I could fathom) to simply detect an overflow if one 
occurs, in lcm (there is a multiplication that really can overflow), 
static or runtime versions.

3) possible truncation problems, in lcm, if the computation in unsigned 
long does not overflow, but the data are actually, say, short, and the 
result is not representable as a short.

4) intermediate computations are done in "unsigned long" in a hardwired 
mode, but it might be interesting to be able to use a bigger type if an 
implementation did provide one, otherwise the computation may lead to 
problems.

5) use of this library for other integer-like type (say a "big 
integer") necesitates to specialise internals of this library for this 
other type, instead of requiring that the new type defines the 
necessary algorithmic behavior; this is bad from an orthogonality point 
of view; this is also the converse of our discussion about sync's 
template template parameter :-)

                        Hubert Holin
                        Hubert.Holin_at_[hidden]