Extending the mpn interface

[David Harvey]

Hi, I just want to add my strong support to the development of an mpz/mpn interface as you describe below. I have needed to do this kind of thing countless times, and I am always forced to compromise between efficiency and portability. This kind of interface will eliminate most of the compromise in most cases.

david

On Feb 16, 2013, at 1:51 AM, Niels Möller wrote:

> nisse at lysator.liu.se (Niels Möller) writes:
> 
>> But I miss some features in the public interface to do this
>> conveniently; both for mpn <-> mpz interoperation, and there are also
>> some mpn functions which would be very useful but which are not part of
>> the public interface.
> 
> I and Torbjörn had a little offline meeting after lunch today. Some
> conclusions:
> 
> 1. We should add a minimal mpz/mpn interface.
> 
> 2. We drop the _ from names.
> 
> 3. We should be a bit more liberal in making mpn functions public.
> 
> Below is a revised draft interface. Comments appreciated. I think I'll
> try to get this in fairly soon.
> 
> I also plan to make additional mpn functions public when I need them,
> also with some advance warning to this list.
> 
> PS. About use of mpz_t internals in gmp-h.in: I see a couple of uses of
> _mp_size, but *no* direct use of _mp_alloc.
> 
> Regards,
> /Niels
> 
> /* Second revision of a minimal mpz/mpn interface. Question: Should we
>   use real functions, inline functions, or macros? */
> 
> /* Read access to mpz numbers. */
> 
> /* Return limb pointer, for read-only operations. Use mpz_size to get
>   the number of limbs. */
> const mp_limb_t *
> mpz_read_limbs (const mpz_srcptr x);
> 
> /* Write access to mpz numbers. */
> 
> /* Get a limb pointer for writing, previous contents may be destroyed.
>   Grows allocation if needed to make room for n limbs. */
> mp_limb_t *
> mpz_write_limbs (mpz_ptr x, mp_size_t n);
> 
> /* Get a limb pointer for writing, previous contents is intact.
>   Grows allocation if needed to make room for n limbs. */
> mp_limb_t *
> mpz_modify_limbs (mpz_ptr x, mp_size_t n);
> 
> /* Adjusts the size after writing, to make x properly normalized. n <
>   0 means negative. Should have abs(n) <= the argument for the
>   preceding mpz_write_limbs or mpz_modify_limbs. Never reallocates x,
>   so the pointer from the earlier mpz_write_limbs/mpz_modify_limbs
>   remains valid. */
> void
> mpz_finish_limbs (mpz_ptr x, mp_size_t n);
> 
> /* Using an mpn number as an mpz. Can be used for read-only access
>   only. x must not be cleared or reallocated. Here and below, xs
>   stands for a signed parameter, where abs(xs) is the size, and xs <
>   0 indicates a negative number. Returns x, cast to const, so it can
>   be used directly as an argument for other mpz functions. */
> mpz_srcptr
> mpz_init_mpn (mpz_ptr x, const mp_limb_t *xp, mp_size_t xs);
> 
> /* Intializer for an mpz_t, having the same effect as calling
>   mpz_init_mpn, but without a function call. It can be used to
>   initialize variables which are statically allocated and/or const.
>   xp would usually be a const mp_limb_t *, but unfortunately, it must
>   then be cast to (mp_limb_t *) for use with this macro. */
> #define MPZ_MPN_INITIALIZER(xp, xs) { { 0, (xs), (xp) } }
> 
> 
> 
> /* Some convenience functions, which we might want to add later. */
> 
> /* Copy x, which must be at most xn limbs, to the {xp, xn} area,
>   zero-padding if needed. Not sure what to do if x is too large to
>   fit, or if x < 0. */
> void
> mpz_get_mpn (mp_limb_t *xp, mp_size_t xn, const mpz_t x);
> 
> /* Assigns x from the area {xp, abs(xs)}. */
> void
> mpz_set_mpn (mpz_t x, const mp_limb_t *xp, mp_size_t xs);
> 
> /* Compares an mpz value to an mpn value. */
> int
> mpz_cmp_mpn (const mpz_t x, const mp_limb_t *yp, mp_size_t ys);
> 
> -- 
> Niels Möller. PGP-encrypted email is preferred. Keyid C0B98E26.
> Internet email is subject to wholesale government surveillance.
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