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/* mpz_prodlimbs(RESULT, V, LEN) -- Set RESULT to V[0]*V[1]*...*V[LEN-1].
Contributed to the GNU project by Marco Bodrato.
THE FUNCTION IN THIS FILE IS INTERNAL WITH A MUTABLE INTERFACE.
IT IS ONLY SAFE TO REACH IT THROUGH DOCUMENTED INTERFACES.
IN FACT, IT IS ALMOST GUARANTEED THAT IT WILL CHANGE OR
DISAPPEAR IN A FUTURE GNU MP RELEASE.
Copyright 2010-2012 Free Software Foundation, Inc.
This file is part of the GNU MP Library.
The GNU MP Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published
by the Free Software Foundation; either version 3 of the License, or (at
your option) any later version.
The GNU MP Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
License for more details.
You should have received a copy of the GNU Lesser General Public License
along with the GNU MP Library. If not, see https://www.gnu.org/licenses/. */
#include "gmp.h"
#include "gmp-impl.h"
/*********************************************************/
/* Section list-prod: product of a list -> mpz_t */
/*********************************************************/
/* FIXME: should be tuned */
#ifndef RECURSIVE_PROD_THRESHOLD
#define RECURSIVE_PROD_THRESHOLD (MUL_TOOM22_THRESHOLD)
#endif
/* Computes the product of the j>1 limbs pointed by factors, puts the
* result in x. It assumes that all limbs are non-zero. Above
* Karatsuba's threshold it uses a binary splitting strategy, to gain
* speed by the asymptotically fast multiplication algorithms.
*
* The list in {factors, j} is overwritten.
* Returns the size of the result
*/
mp_size_t
mpz_prodlimbs (mpz_ptr x, mp_ptr factors, mp_size_t j)
{
mp_limb_t cy;
mp_size_t size, i;
mp_ptr prod;
ASSERT (j > 1);
ASSERT (RECURSIVE_PROD_THRESHOLD > 3);
if (BELOW_THRESHOLD (j, RECURSIVE_PROD_THRESHOLD)) {
j--;
size = 1;
for (i = 1; i < j; i++)
{
cy = mpn_mul_1 (factors, factors, size, factors[i]);
factors[size] = cy;
size += cy != 0;
};
prod = MPZ_NEWALLOC (x, size + 1);
cy = mpn_mul_1 (prod, factors, size, factors[i]);
prod[size] = cy;
return SIZ (x) = size + (cy != 0);
} else {
mpz_t x1, x2;
TMP_DECL;
i = j >> 1;
j -= i;
TMP_MARK;
MPZ_TMP_INIT (x2, j);
PTR (x1) = factors + i;
ALLOC (x1) = j;
j = mpz_prodlimbs (x2, factors + i, j);
i = mpz_prodlimbs (x1, factors, i);
size = i + j;
prod = MPZ_NEWALLOC (x, size);
if (i >= j)
cy = mpn_mul (prod, PTR(x1), i, PTR(x2), j);
else
cy = mpn_mul (prod, PTR(x2), j, PTR(x1), i);
TMP_FREE;
return SIZ (x) = size - (cy == 0);
}
}
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