
- prime_count - needs the pc(#) option as well as pc(#,#)

- Do a GMP version of LMO prime_count.  Possible versions:
    - 32-bit main, 16-bit support
    - 64-bit main, 32-bit support   (using __uint64_t if necessary)
    - 128-bit main, 64-bit support  (gcc only)
    - GMP main, 32-bit support      (portable)
    - GMP main, 64-bit support      (mostly portable)

- nth_prime

- GMP SQUFOF could use a better implementation, though low priority since it
  just isn't going to be the right algorithm for numbers > 2^64.  Mainly what
  it needs is to pay attention to the rounds argument.  Perhaps race.

- Tune and improve SIMPQS for our uses.  Check FLINT 2.3 for improvements.

- Write our own QS.

- The statics in ecm and QS won't play well with threading.

- ECPP: Perhaps more HCPs/WCPs could be loaded if needed?

- ECPP: Another idea is related to Atkin/Morain's EAS.  When we have a large
  number, we can process more Ds, delaying the downrun.  We then use the
  smallest q we found.  Combine with lightened stage 1 factoring as above.
  This drops our q sizes faster, at the expense of more up-front time.
  I have this running, but for small numbers it doesn't matter much, and for
  large numbers it just highlights how much nicer FAS would be.

- ECPP: All discriminants with D % 8 != 3 have been converted to Weber.  We're
  still left with lots of those D values.  Figure out a different invariant
  that will make smaller polynomials, along with a root conversion.

- ECPP: Add a fast BLS5 to downrun?

- Add BLS17 proof.  Merge into BLS5 code since the end is the same.

- Add tests for proofs, similar to MPU t/23.

- Handle objects of type:
     Math::GMP
     Math::GMP::Fast
     Math::GMPz
  We should parse their mpz_t directly, do our processing, and output the
  result as one of these types.

- Recognize Math::BigInt / Math::Pari objects.  Shortcut validation.
  Create results as new objects of their type.

- These functions should be added:
     legendre_phi
     znlog

- Any fast primality pretest would be nice.  I've tested:
    - Colin Plumb's Euler Criterion test
    - Fermat base 210, which is done in GMP's internal millerrabin.c.
    - Fermat base 2 also no faster than SPRP-2, though some claim it is.
      mpz_t e, r;  int composite;
      mpz_init(e);
      mpz_init_set_ui(r, 2);  mpz_sub_ui(e, n, 1);  mpz_powm(r, r, e, n);
      composite = mpz_cmp_ui(r, 1) != 0;
      mpz_clear(r); mpz_clear(e);
      if (composite) return 0;
  None of these are faster on average than just doing BPSW.

- merge the two frobenius tests.  cp is faster, needs the deterministic
  version, we should switch to the two input version (allow GMP), etc.

- New version of Pi code using Chudnovsky.  See Pari.

- tests for sieve_primes.

- speed up range sieving.

- fast prime printing routine.  The following could be trivially 2x faster:
    $n = 10**20; say for Math::Prime::Util::GMP::sieve_primes($n,$n+8e9,0);
  About 3 minutes vs. 7-8 just by using gmp_printf.
  Using sieve_range doesn't help, as the issue is the massive return array.

- More efficient version of ramanujan_tau?  MPU has an hclassno implementation
  now.

- Consider ranged ramanujan_tau.  See:
  https://cs.uwaterloo.ca/journals/JIS/VOL13/Lygeros/lygeros5.pdf
  Where we could compute a number of hclassno values, then generate the
  tau values.  This might be more efficient.

- We could do LLR and Proth in prob_prime and return 1 instead of 2, leaving
  certs possible.

- consider probabilistic is_primitive_root for large inputs

- Verify speed and memory use of GMP's two binomials for various versions
  and compare.  Looks like Luschny sent his changes after 5.0.0.
  https://gmplib.org/list-archives/gmp-discuss/2010-February/004036.html

- faster znprimroot

- Identify places where 32-bit GMP on 64-bit Perl will trip us up.

- BLS75 methods: check if we can return 0 instead of 1 in many cases.

- Make a trial factor routine that returns all factors.  This can be done
  with a single treesieve.  ECPP could make use of this (since it is doing
  many calls, keeping the product tree around would be useful).
  All current calls are testing primality, so don't need multiple returns.
  Changing the XS call to return multiple values might be useful.

- mpu 'use bigint; $n=14299; say is_prime($n); say Math::Prime::Util::GMP::is_nplus1_prime($n)'
  n=14299  F2=52 R2=275.  s=3,r=-37.  This passes theorem 17.
  qi=2  p=66,q=2,d=4348
  qi=13 p=45,q=1,d=2021
  5543 also
  all examples of this seem to be n+1 = 2 * [many small factors]

  n = 5543 = 23*241, n+1=5544
  n+1 = F2 * R2 = 88 * 63.  R2>1.  gcd(F2,R2)=1.
  q_1 = 2    p=19,q=5,d=341
  q_2 = 11   p=18,q=50,d=124
  By Corollary 8, N is prime.
  By Theorem 17, N is prime.
  r2 = 63    p=11,q=29,d=5
  By Corollary 10, N is prime
  By Theorem 19, N is prime

- zeta below -3
