mpz_limbs interface

[Torbjorn Granlund]

nisse at lysator.liu.se (Niels Möller) writes:

  I see. In this particular case, I think the right gmp interface change
  is to add mpn_urandomb and mpn_rrandomb (similar to current mpn_random
  and mpn_random2, but with a randstate argument). If I understand this
  correctly, the main obstacle is that random number internals use mpz
  functions, which is an undesirable dependency for mpn functions.
  
We should indeed do this.

The random number framework uses the following mpz functions:

    mpz_add_ui
    mpz_addmul_ui
    mpz_clear
    mpz_clrbit
    mpz_export
    mpz_fdiv_r_2exp
    mpz_init
    mpz_init2
    mpz_init_set
    mpz_init_set_str
    mpz_mod
    mpz_mul
    mpz_setbit
    mpz_sub_ui
    mpz_tdiv_q_2exp
    mpz_tdiv_r_2exp
    mpz_tstbit

This should be fairly easy to rewrite to use mpn.  For testing the
result, I'd write a wrapper C program that run old and new code in
separate processes, and compare that the results are identical for the
same (now and then regenerated) seeds.

There is a pseudo-dependency on mpz in the gmp_randstate_t type, since
the _mp_seed if of type mpz_t.  To clean that up without causing binary
incompatibility, we could just define a type with the exact same
components as mpz_t.


Torbjörn
Please encrypt, key id 0xC8601622