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

     1  /* mpz_urandomm (rop, state, n) -- Generate a uniform pseudorandom
     2     integer in the range 0 to N-1, using STATE as the random state
     3     previously initialized by a call to gmp_randinit().
     4  
     5  Copyright 2000, 2002, 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  #include "longlong.h" /* for count_leading_zeros */
    36  
    37  
    38  #define MAX_URANDOMM_ITER  80
    39  
    40  void
    41  mpz_urandomm (mpz_ptr rop, gmp_randstate_t rstate, mpz_srcptr n)
    42  {
    43    mp_ptr rp, np, nlast;
    44    mp_size_t nbits, size;
    45    int count;
    46    int pow2;
    47    int cmp;
    48    TMP_DECL;
    49  
    50    size = ABSIZ (n);
    51    if (UNLIKELY (size == 0))
    52      DIVIDE_BY_ZERO;
    53  
    54    nlast = &PTR (n)[size - 1];
    55  
    56    /* Detect whether n is a power of 2.  */
    57    pow2 = POW2_P (*nlast);
    58    if (pow2 != 0)
    59      for (np = PTR (n); np < nlast; np++)
    60        if (*np != 0)
    61  	{
    62  	  pow2 = 0;		/* Mark n as `not a power of two'.  */
    63  	  break;
    64  	}
    65  
    66    count_leading_zeros (count, *nlast);
    67    nbits = size * GMP_NUMB_BITS - (count - GMP_NAIL_BITS) - pow2;
    68    if (nbits == 0)		/* nbits == 0 means that n was == 1.  */
    69      {
    70        SIZ (rop) = 0;
    71        return;
    72      }
    73  
    74    TMP_MARK;
    75    np = PTR (n);
    76    if (rop == n)
    77      {
    78        mp_ptr tp;
    79        tp = TMP_ALLOC_LIMBS (size);
    80        MPN_COPY (tp, np, size);
    81        np = tp;
    82      }
    83  
    84    /* Here the allocated size can be one too much if n is a power of
    85       (2^GMP_NUMB_BITS) but it's convenient for using mpn_cmp below.  */
    86    rp = MPZ_REALLOC (rop, size);
    87    /* Clear last limb to prevent the case in which size is one too much.  */
    88    rp[size - 1] = 0;
    89  
    90    count = MAX_URANDOMM_ITER;	/* Set iteration count limit.  */
    91    do
    92      {
    93        _gmp_rand (rp, rstate, nbits);
    94        MPN_CMP (cmp, rp, np, size);
    95      }
    96    while (cmp >= 0 && --count != 0);
    97  
    98    if (count == 0)
    99      /* Too many iterations; return result mod n == result - n */
   100      mpn_sub_n (rp, rp, np, size);
   101  
   102    MPN_NORMALIZE (rp, size);
   103    SIZ (rop) = size;
   104    TMP_FREE;
   105  }