Extending the mpn interface
Niels Möller
nisse at lysator.liu.se
Wed Jan 30 22:19:40 CET 2013
Emmanuel Thomé <emmanuel.thome at gmail.com> writes:
> I've too been traveling with MPZ_SET_MPN, MPN_SET_MPZ, MPN_NORMALIZE
> macros/functions and so on, for quite some time now.
Here's a sketch (totally untested, not even compiled), supporting the
operations I have seen a need for. As usual, good naming is the
difficult part ;-)
I think it makes some sense to use an _mpz prefix on the functions,
following _mpz_realloc rather than mpz_size.
Regards,
/Niels
/* Some functions for interfacing between mpz and mpn code. Signs of
the mpz numbers are generally ignored. */
/* We already have mpz_size (which might be better named _mpz_size).
And _mpz_realloc, which isn't quite what we need, but which could
be used to implement this interface without relying on the
MPZ_*ALLOC macros. */
/* This could be rewritten to access _mp_size and _mp_d (but not
_mp_alloc) directly, and use _mpz_realloc for increasing allocation
size when needed. That should be fairly portable between GMP
releases, I think. */
/* Read access to mpz numbers. */
/* Return limb pointer, for read-only operations. Use mpz_size to get
the number of limbs. */
mp_srcptr
_mpz_read_limbs (const mpz_t x)
{
return PTR (x);
}
/* Get a pointer to an n limb area, for read-only operation. n must be
greater or equal to the current size, and the mpz is zero-padded if
needed. */
mp_srcptr
_mpz_read_limbs_n (mpz_t x, mp_size_t n)
{
mp_size_t xn = ABSSIZ (x);
mp_ptr xp;
ASSERT (xn <= n);
xp = MPZ_REALLOC (x, n);
if (xn < n)
mpn_zero (xp + xn, n - xn);
return xp;
}
/* Write access to mpz numbers. */
/* Get a limb pointer for writing, previous contents may be
destroyed. */
mpz_ptr
_mpz_write_limbs (mpz_t x, mp_size_t n)
{
ASSERT (n > 0);
return MPZ_NEWALLOC (x, n);
}
/* Get a limb pointer for writing, previous contents is intact. */
mpz_ptr
_mpz_modify_limbs (mpz_t x, mp_size_t n)
{
ASSERT (n > 0);
return MPZ_REALLOC (x, n);
}
void
_mpz_done_limbs (mpz_t x, mp_size_t n)
{
ASSERT (n >= 0);
MPN_NORMALIZE (PTR (x), n);
SIZ (x) = n;
}
/* Using an mpn number as an mpz. Can be used for read-only access
only. x must not be cleared or reallocated. I'd like to mark the
date as const in some way, but that won't quite work. */
void
_mpz_init_mpn (mpz_t x, mp_ptr *xp, mp_size_t xs)
{
mp_size_t xn = ABS (xs);
MPN_NORMALIZE (x, xn);
x->_mp_size = xs < 0 ? -xn : xn;
x->_mp_alloc = 0;
x->_mp_d = xp;
}
--
Niels Möller. PGP-encrypted email is preferred. Keyid C0B98E26.
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