github.com/aergoio/aergo@v1.3.1/libtool/src/gmp-6.1.2/mpz/lucnum2_ui.c (about)

     1  /* mpz_lucnum2_ui -- calculate Lucas numbers.
     2  
     3  Copyright 2001, 2003, 2005, 2012 Free Software Foundation, Inc.
     4  
     5  This file is part of the GNU MP Library.
     6  
     7  The GNU MP Library is free software; you can redistribute it and/or modify
     8  it under the terms of either:
     9  
    10    * the GNU Lesser General Public License as published by the Free
    11      Software Foundation; either version 3 of the License, or (at your
    12      option) any later version.
    13  
    14  or
    15  
    16    * the GNU General Public License as published by the Free Software
    17      Foundation; either version 2 of the License, or (at your option) any
    18      later version.
    19  
    20  or both in parallel, as here.
    21  
    22  The GNU MP Library is distributed in the hope that it will be useful, but
    23  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
    24  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
    25  for more details.
    26  
    27  You should have received copies of the GNU General Public License and the
    28  GNU Lesser General Public License along with the GNU MP Library.  If not,
    29  see https://www.gnu.org/licenses/.  */
    30  
    31  #include <stdio.h>
    32  #include "gmp.h"
    33  #include "gmp-impl.h"
    34  
    35  
    36  void
    37  mpz_lucnum2_ui (mpz_ptr ln, mpz_ptr lnsub1, unsigned long n)
    38  {
    39    mp_ptr     lp, l1p, f1p;
    40    mp_size_t  size;
    41    mp_limb_t  c;
    42    TMP_DECL;
    43  
    44    ASSERT (ln != lnsub1);
    45  
    46    /* handle small n quickly, and hide the special case for L[-1]=-1 */
    47    if (n <= FIB_TABLE_LUCNUM_LIMIT)
    48      {
    49        mp_limb_t  f  = FIB_TABLE (n);
    50        mp_limb_t  f1 = FIB_TABLE ((int) n - 1);
    51  
    52        /* L[n] = F[n] + 2F[n-1] */
    53        PTR(ln)[0] = f + 2*f1;
    54        SIZ(ln) = 1;
    55  
    56        /* L[n-1] = 2F[n] - F[n-1], but allow for L[-1]=-1 */
    57        PTR(lnsub1)[0] = (n == 0 ? 1 : 2*f - f1);
    58        SIZ(lnsub1) = (n == 0 ? -1 : 1);
    59  
    60        return;
    61      }
    62  
    63    TMP_MARK;
    64    size = MPN_FIB2_SIZE (n);
    65    f1p = TMP_ALLOC_LIMBS (size);
    66  
    67    lp  = MPZ_REALLOC (ln,     size+1);
    68    l1p = MPZ_REALLOC (lnsub1, size+1);
    69  
    70    size = mpn_fib2_ui (l1p, f1p, n);
    71  
    72    /* L[n] = F[n] + 2F[n-1] */
    73  #if HAVE_NATIVE_mpn_addlsh1_n
    74    c = mpn_addlsh1_n (lp, l1p, f1p, size);
    75  #else
    76    c = mpn_lshift (lp, f1p, size, 1);
    77    c += mpn_add_n (lp, lp, l1p, size);
    78  #endif
    79    lp[size] = c;
    80    SIZ(ln) = size + (c != 0);
    81  
    82    /* L[n-1] = 2F[n] - F[n-1] */
    83    c = mpn_lshift (l1p, l1p, size, 1);
    84    c -= mpn_sub_n (l1p, l1p, f1p, size);
    85    ASSERT ((mp_limb_signed_t) c >= 0);
    86    l1p[size] = c;
    87    SIZ(lnsub1) = size + (c != 0);
    88  
    89    TMP_FREE;
    90  }