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

     1  /* mpz_fac_ui(RESULT, N) -- Set RESULT to N!.
     2  
     3  Contributed to the GNU project by Marco Bodrato.
     4  
     5  Copyright 1991, 1993-1995, 2000-2003, 2011, 2012 Free Software Foundation, Inc.
     6  
     7  This file is part of the GNU MP Library.
     8  
     9  The GNU MP Library is free software; you can redistribute it and/or modify
    10  it under the terms of either:
    11  
    12    * the GNU Lesser General Public License as published by the Free
    13      Software Foundation; either version 3 of the License, or (at your
    14      option) any later version.
    15  
    16  or
    17  
    18    * the GNU General Public License as published by the Free Software
    19      Foundation; either version 2 of the License, or (at your option) any
    20      later version.
    21  
    22  or both in parallel, as here.
    23  
    24  The GNU MP Library is distributed in the hope that it will be useful, but
    25  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
    26  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
    27  for more details.
    28  
    29  You should have received copies of the GNU General Public License and the
    30  GNU Lesser General Public License along with the GNU MP Library.  If not,
    31  see https://www.gnu.org/licenses/.  */
    32  
    33  #include "gmp.h"
    34  #include "gmp-impl.h"
    35  
    36  #define FACTOR_LIST_STORE(P, PR, MAX_PR, VEC, I)		\
    37    do {								\
    38      if ((PR) > (MAX_PR)) {					\
    39        (VEC)[(I)++] = (PR);					\
    40        (PR) = (P);						\
    41      } else							\
    42        (PR) *= (P);						\
    43    } while (0)
    44  
    45  #if TUNE_PROGRAM_BUILD
    46  #define FACTORS_PER_LIMB (GMP_NUMB_BITS / (LOG2C(FAC_DSC_THRESHOLD_LIMIT-1)+1))
    47  #else
    48  #define FACTORS_PER_LIMB (GMP_NUMB_BITS / (LOG2C(FAC_ODD_THRESHOLD)+1))
    49  #endif
    50  
    51  /* Computes n!, the factorial of n.
    52     WARNING: it assumes that n fits in a limb!
    53   */
    54  void
    55  mpz_fac_ui (mpz_ptr x, unsigned long n)
    56  {
    57    static const mp_limb_t table[] = { ONE_LIMB_FACTORIAL_TABLE };
    58  
    59    ASSERT (n <= GMP_NUMB_MAX);
    60  
    61    if (n < numberof (table))
    62      {
    63        PTR (x)[0] = table[n];
    64        SIZ (x) = 1;
    65      }
    66    else if (BELOW_THRESHOLD (n, FAC_ODD_THRESHOLD))
    67      {
    68        mp_limb_t prod, max_prod;
    69        mp_size_t j;
    70        mp_ptr    factors;
    71        TMP_SDECL;
    72  
    73        TMP_SMARK;
    74        factors = TMP_SALLOC_LIMBS (2 + (n - numberof (table)) / FACTORS_PER_LIMB);
    75  
    76        factors[0] = table[numberof (table)-1];
    77        j = 1;
    78        prod = n;
    79  #if TUNE_PROGRAM_BUILD
    80        max_prod = GMP_NUMB_MAX / FAC_DSC_THRESHOLD_LIMIT;
    81  #else
    82        max_prod = GMP_NUMB_MAX / (FAC_ODD_THRESHOLD | 1);
    83  #endif
    84        while (--n >= numberof (table))
    85  	FACTOR_LIST_STORE (n, prod, max_prod, factors, j);
    86  
    87        factors[j++] = prod;
    88        mpz_prodlimbs (x, factors, j);
    89  
    90        TMP_SFREE;
    91      }
    92    else
    93      {
    94        mp_limb_t count;
    95        mpz_oddfac_1 (x, n, 0);
    96        if (n <= TABLE_LIMIT_2N_MINUS_POPC_2N)
    97  	count = __gmp_fac2cnt_table[n / 2 - 1];
    98        else
    99  	{
   100  	  popc_limb (count, n);
   101  	  count = n - count;
   102  	}
   103        mpz_mul_2exp (x, x, count);
   104      }
   105  }
   106  
   107  #undef FACTORS_PER_LIMB
   108  #undef FACTOR_LIST_STORE