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      1 /* mpz_prodlimbs(RESULT, V, LEN) -- Set RESULT to V[0]*V[1]*...*V[LEN-1].
      2 
      3 Contributed to the GNU project by Marco Bodrato.
      4 
      5 THE FUNCTION IN THIS FILE IS INTERNAL WITH A MUTABLE INTERFACE.
      6 IT IS ONLY SAFE TO REACH IT THROUGH DOCUMENTED INTERFACES.
      7 IN FACT, IT IS ALMOST GUARANTEED THAT IT WILL CHANGE OR
      8 DISAPPEAR IN A FUTURE GNU MP RELEASE.
      9 
     10 Copyright 2010-2012 Free Software Foundation, Inc.
     11 
     12 This file is part of the GNU MP Library.
     13 
     14 The GNU MP Library is free software; you can redistribute it and/or modify
     15 it under the terms of either:
     16 
     17   * the GNU Lesser General Public License as published by the Free
     18     Software Foundation; either version 3 of the License, or (at your
     19     option) any later version.
     20 
     21 or
     22 
     23   * the GNU General Public License as published by the Free Software
     24     Foundation; either version 2 of the License, or (at your option) any
     25     later version.
     26 
     27 or both in parallel, as here.
     28 
     29 The GNU MP Library is distributed in the hope that it will be useful, but
     30 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
     31 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
     32 for more details.
     33 
     34 You should have received copies of the GNU General Public License and the
     35 GNU Lesser General Public License along with the GNU MP Library.  If not,
     36 see https://www.gnu.org/licenses/.  */
     37 
     38 #include "gmp-impl.h"
     39 
     40 /*********************************************************/
     41 /* Section list-prod: product of a list -> mpz_t         */
     42 /*********************************************************/
     43 
     44 /* FIXME: should be tuned */
     45 #ifndef RECURSIVE_PROD_THRESHOLD
     46 #define RECURSIVE_PROD_THRESHOLD (MUL_TOOM22_THRESHOLD)
     47 #endif
     48 
     49 /* Computes the product of the j>1 limbs pointed by factors, puts the
     50  * result in x. It assumes that all limbs are non-zero. Above
     51  * Karatsuba's threshold it uses a binary splitting strategy, to gain
     52  * speed by the asymptotically fast multiplication algorithms.
     53  *
     54  * The list in  {factors, j} is overwritten.
     55  * Returns the size of the result
     56  */
     57 
     58 mp_size_t
     59 mpz_prodlimbs (mpz_ptr x, mp_ptr factors, mp_size_t j)
     60 {
     61   mp_limb_t cy;
     62   mp_size_t size, i;
     63   mp_ptr    prod;
     64 
     65   ASSERT (j > 1);
     66   ASSERT (RECURSIVE_PROD_THRESHOLD > 3);
     67 
     68   if (BELOW_THRESHOLD (j, RECURSIVE_PROD_THRESHOLD)) {
     69     j--;
     70     size = 1;
     71 
     72     for (i = 1; i < j; i++)
     73       {
     74 	cy = mpn_mul_1 (factors, factors, size, factors[i]);
     75 	factors[size] = cy;
     76 	size += cy != 0;
     77       };
     78 
     79     prod = MPZ_NEWALLOC (x, size + 1);
     80 
     81     cy = mpn_mul_1 (prod, factors, size, factors[i]);
     82     prod[size] = cy;
     83     return SIZ (x) = size + (cy != 0);
     84   } else {
     85     mpz_t x1, x2;
     86     TMP_DECL;
     87 
     88     i = j >> 1;
     89     j -= i;
     90     TMP_MARK;
     91 
     92     MPZ_TMP_INIT (x2, j);
     93 
     94     PTR (x1) = factors + i;
     95     ALLOC (x1) = j;
     96     j = mpz_prodlimbs (x2, factors + i, j);
     97     i = mpz_prodlimbs (x1, factors, i);
     98     size = i + j;
     99     prod = MPZ_NEWALLOC (x, size);
    100     if (i >= j)
    101       cy = mpn_mul (prod, PTR(x1), i, PTR(x2), j);
    102     else
    103       cy = mpn_mul (prod, PTR(x2), j, PTR(x1), i);
    104     TMP_FREE;
    105 
    106     return SIZ (x) = size - (cy == 0);
    107   }
    108 }
    109