github.com/aergoio/aergo@v1.3.1/libtool/src/gmp-6.1.2/mpn/generic/toom_eval_pm2.c (about)

     1  /* mpn_toom_eval_pm2 -- Evaluate a polynomial in +2 and -2
     2  
     3     Contributed to the GNU project by Niels Möller and Marco Bodrato
     4  
     5     THE FUNCTION IN THIS FILE IS INTERNAL WITH A MUTABLE INTERFACE.  IT IS ONLY
     6     SAFE TO REACH IT THROUGH DOCUMENTED INTERFACES.  IN FACT, IT IS ALMOST
     7     GUARANTEED THAT IT WILL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE.
     8  
     9  Copyright 2009 Free Software Foundation, Inc.
    10  
    11  This file is part of the GNU MP Library.
    12  
    13  The GNU MP Library is free software; you can redistribute it and/or modify
    14  it under the terms of either:
    15  
    16    * the GNU Lesser General Public License as published by the Free
    17      Software Foundation; either version 3 of the License, or (at your
    18      option) any later version.
    19  
    20  or
    21  
    22    * the GNU General Public License as published by the Free Software
    23      Foundation; either version 2 of the License, or (at your option) any
    24      later version.
    25  
    26  or both in parallel, as here.
    27  
    28  The GNU MP Library is distributed in the hope that it will be useful, but
    29  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
    30  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
    31  for more details.
    32  
    33  You should have received copies of the GNU General Public License and the
    34  GNU Lesser General Public License along with the GNU MP Library.  If not,
    35  see https://www.gnu.org/licenses/.  */
    36  
    37  #include "gmp.h"
    38  #include "gmp-impl.h"
    39  
    40  /* DO_addlsh2(d,a,b,n,cy) computes cy,{d,n} <- {a,n} + 4*(cy,{b,n}), it
    41     can be used as DO_addlsh2(d,a,d,n,d[n]), for accumulation on {d,n+1}. */
    42  #if HAVE_NATIVE_mpn_addlsh2_n
    43  #define DO_addlsh2(d, a, b, n, cy)	\
    44  do {					\
    45    (cy) <<= 2;				\
    46    (cy) += mpn_addlsh2_n(d, a, b, n);	\
    47  } while (0)
    48  #else
    49  #if HAVE_NATIVE_mpn_addlsh_n
    50  #define DO_addlsh2(d, a, b, n, cy)	\
    51  do {					\
    52    (cy) <<= 2;				\
    53    (cy) += mpn_addlsh_n(d, a, b, n, 2);	\
    54  } while (0)
    55  #else
    56  /* The following is not a general substitute for addlsh2.
    57     It is correct if d == b, but it is not if d == a.  */
    58  #define DO_addlsh2(d, a, b, n, cy)	\
    59  do {					\
    60    (cy) <<= 2;				\
    61    (cy) += mpn_lshift(d, b, n, 2);	\
    62    (cy) += mpn_add_n(d, d, a, n);	\
    63  } while (0)
    64  #endif
    65  #endif
    66  
    67  /* Evaluates a polynomial of degree 2 < k < GMP_NUMB_BITS, in the
    68     points +2 and -2. */
    69  int
    70  mpn_toom_eval_pm2 (mp_ptr xp2, mp_ptr xm2, unsigned k,
    71  		   mp_srcptr xp, mp_size_t n, mp_size_t hn, mp_ptr tp)
    72  {
    73    int i;
    74    int neg;
    75    mp_limb_t cy;
    76  
    77    ASSERT (k >= 3);
    78    ASSERT (k < GMP_NUMB_BITS);
    79  
    80    ASSERT (hn > 0);
    81    ASSERT (hn <= n);
    82  
    83    /* The degree k is also the number of full-size coefficients, so
    84     * that last coefficient, of size hn, starts at xp + k*n. */
    85  
    86    cy = 0;
    87    DO_addlsh2 (xp2, xp + (k-2) * n, xp + k * n, hn, cy);
    88    if (hn != n)
    89      cy = mpn_add_1 (xp2 + hn, xp + (k-2) * n + hn, n - hn, cy);
    90    for (i = k - 4; i >= 0; i -= 2)
    91      DO_addlsh2 (xp2, xp + i * n, xp2, n, cy);
    92    xp2[n] = cy;
    93  
    94    k--;
    95  
    96    cy = 0;
    97    DO_addlsh2 (tp, xp + (k-2) * n, xp + k * n, n, cy);
    98    for (i = k - 4; i >= 0; i -= 2)
    99      DO_addlsh2 (tp, xp + i * n, tp, n, cy);
   100    tp[n] = cy;
   101  
   102    if (k & 1)
   103      ASSERT_NOCARRY(mpn_lshift (tp , tp , n + 1, 1));
   104    else
   105      ASSERT_NOCARRY(mpn_lshift (xp2, xp2, n + 1, 1));
   106  
   107    neg = (mpn_cmp (xp2, tp, n + 1) < 0) ? ~0 : 0;
   108  
   109  #if HAVE_NATIVE_mpn_add_n_sub_n
   110    if (neg)
   111      mpn_add_n_sub_n (xp2, xm2, tp, xp2, n + 1);
   112    else
   113      mpn_add_n_sub_n (xp2, xm2, xp2, tp, n + 1);
   114  #else /* !HAVE_NATIVE_mpn_add_n_sub_n */
   115    if (neg)
   116      mpn_sub_n (xm2, tp, xp2, n + 1);
   117    else
   118      mpn_sub_n (xm2, xp2, tp, n + 1);
   119  
   120    mpn_add_n (xp2, xp2, tp, n + 1);
   121  #endif /* !HAVE_NATIVE_mpn_add_n_sub_n */
   122  
   123    ASSERT (xp2[n] < (1<<(k+2))-1);
   124    ASSERT (xm2[n] < ((1<<(k+3))-1 - (1^k&1))/3);
   125  
   126    neg ^= ((k & 1) - 1);
   127  
   128    return neg;
   129  }
   130  
   131  #undef DO_addlsh2