speed of unbalanced multiplication

[Torbjorn Granlund]

Zimmermann Paul <Paul.Zimmermann at loria.fr> writes:

  in GMP 5.1.0, a multiplication of n x m limbs for m < n can be slower than
  a multiplication of n x n limbs. Compare for example the line starting with
  775660 in the first output from speed, and the one starting with 1000000 in
  the second one below.
  
  [snip]

  This is quite embarrassing, especially when one optimizes an algorithm by
  reducing the multiplications sizes, and the algorithm gets slower...
  
I think "quite embarrassing" is an exaggeration for a 2% slowdown...

But sure, there is room for further improvement of the multiplication
code.  We have new code, see e.g. <http://gmplib.org:8000/gcd-nisse/>
which have the potential of smoothing things out.

-- 
Torbjörn