a function to get multiplication threshold?
Wed, 18 Dec 2002 10:05:30 +1000
Serge Winitzki <email@example.com> writes:
> I was trying to see at what precision GMP is starting to use
> subquadratic multiplication and realized that this is currently an
> implementation detail that is not exposed to the users.
> However I think it's a useful piece of information to have.
Alas I don't think should be done, it's highly implementation
> I have been writing
> arbitrary-precision algorithms for various special functions and there
> is frequently a choice between algorithms that depends on the speed of
> the multiple-precision multiplication.
You'll be best off doing some measuring of the alternatives, and
making a tuned threshold for your algorithm, like the thresholds
You could try using some of the stuff in tune/libspeed.la.
speed_measure is the best, but it's a bit tricky. speed_starttime and
speed_endtime are easy, and still give the benefit of the various
measuring methods we know for different systems.
> SQR_KARATSUBA_THRESHOLD and MUL_KARATSUBA_THRESHOLD (the
> former is probably always larger than the latter),
Yes, generally. But we treat the two independently and let them fall
out from the measurments.