(First of all, I'm a GSL neophyte. Okay, enough apologizing.)
I'm trying to see how aggressive I can turn Sun Studio compiler
optimizations on with GSL.
Here is one of my problems. Aggressive optimizations can bypass the
intentions of gsl_log1p() in sys/log1p.c:
double gsl_log1p (const double x)
{
volatile double y;
y = 1 + x;
return log(y) - ((y-1)-x)/y ; /* cancels errors with IEEE arithmetic */
}
That's very nicely written, but an aggressive compiler can rewrite that
as y-(1+x) and so you lose the impact of what you had hoped to
accomplish with precomputing 1+x and assigning it to a volatile variable.
REQUEST #1: Ruggedize the computation yet further than is already done.
E.g.,
double gsl_log1p (const double x)
{
volatile double y, z;
y = 1 + x;
z = y - 1;
return log(y) - (z-x)/y ; /* cancels errors with IEEE arithmetic */
}
But there is another issue. The fact that gsl_log1p() wasn't generating
the expected result shouldn't have been a problem in the first place.
The system provides log1p() and gsl_log1p() is never actually even
used. Despite that, "make check" and sys/test.c test the
otherwise-never-used gsl_log1p().
REQUEST #2: Change the check procedures so that unused functions are
not tested. E.g., when you "make check", have sys/test.c test only
those gsl_*() functions that will actually be used by GSL.
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