Re: forprime in arithmetic progressions?

[Karim Belabas <Karim.Belabas@math.u-bordeaux.fr>]

* Charles Greathouse [2018-02-28 20:13]:
> The prime iterator (u_forprime_arith_init etc.) internally works in
> arithmetic progressions. Would it be possible to expose this to the user?
> (Perhaps "forprimestep", or maybe an optional final (INTMOD) argument to
> forprime like prod.)
> 
> This would be useful, not very hard to implement, and can't be efficiently
> duplicated in gp.

A first attempt is now committed to the 'master' branch. Please test !

The following two syntaxes are supported:
 ? forprimestep(p = 4, 40, 3, print(p))
 7
 13
 19
 31
 37
 ? forprimestep(p = 4, 40, Mod(2,3), print(p))
 5
 11
 17
 23
 29

Notes :

- The implementation is currently not very efficient : forprime() sieves are
not supported yet [ as in the underlying u_forprime_arith_init ].

- The common difference in the arithmetic progression is restricted to an
unsigned integer (i.e < 2^32 or 2^64)

Cheers,

    K.B.
--
Karim Belabas, IMB (UMR 5251)  Tel: (+33) (0)5 40 00 26 17
Universite de Bordeaux         Fax: (+33) (0)5 40 00 21 23
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