Help stabilising mini-gmp

[Torbjörn Granlund]

"Marco Bodrato" <bodrato at mail.dm.unipi.it> writes:

  I tried the test on a 18-years old 32-bits CPU I'm currently using. A
  single 8000-bit Miller-Rabin round took 20 seconds with mini-gmp.
  That's why I reduced the size. With 2000-bit operands I assume the worst
  execution time will be reduced by a factor 18.
  
  The hypothesis "its time varies hugely" is surely true. Before the
  changeset 17099, on my machine, fluctuations between 2 and 60 seconds
  where the norm. Of course a seed that require many MR rounds on big
  operands is unlikely...
  
I see.  I am less worried now.  Let's mark the bug as done!

If hugely varying operand sizes are motivated (which is the case for
"big"-GMP with its many operand size dependent algorithm choices) one
could make operand size selection more complex to allow good coverage
and less time fluctuations.  One trick is to make random sizes within a
series of, fixed intervals.  I did that for mpz/t-mul.c some years ago.

I have some vague plans of writing a new test framework where that would
be a fundamental mechanims.  One other feature is allowing truly huge
operands, something we currently don't test.

-- 
Torbjörn
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