mpz_prevprime

[Niels Möller]

Seth Troisi <braintwo at gmail.com> writes:

> I modified the patch a tiny bit. Still hoping to get this in for an
> upcoming prime-gap search project.

Looks pretty good to me.

> +static int
> +findnext (mpz_ptr p,
> +          unsigned long(*nextmod_func)(const mpz_t, unsigned long),
> +          void(*nextseq_func)(mpz_t, const mpz_t, unsigned long))

I'd name the function pointer arguments to be more similar to functions
they refer to, and without the "next" and "_func" parts. Maybe mod_ui
and add_ui/incr_ui/update_ui?

And is there a good reason you need different mod functions? I haven't
been following along closely, so I don't know why the current code uses
mpz_cdiv_ui rather than mpz_fdiv_ui. It would make things a bit simpler
if we could use mpz_fdiv_ui (the standard mathematical mod operation)
always.

> +int
> +mpz_prevprime (mpz_ptr p, mpz_srcptr n)

Interface looks good to me. And if we later add a function to find the
first prime in an arithmetic progression, I think that should fit well.

Regards,
/Niels

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