1  /* mpfr_urandomb (rop, state, nbits) -- Generate a uniform pseudorandom
       2     real number between 0 (inclusive) and 1 (exclusive) of size NBITS,
       3     using STATE as the random state previously initialized by a call to
       4     gmp_randinit_lc_2exp_size().
       5  
       6  Copyright 2000-2004, 2006-2023 Free Software Foundation, Inc.
       7  Contributed by the AriC and Caramba projects, INRIA.
       8  
       9  This file is part of the GNU MPFR Library.
      10  
      11  The GNU MPFR Library is free software; you can redistribute it and/or modify
      12  it under the terms of the GNU Lesser General Public License as published by
      13  the Free Software Foundation; either version 3 of the License, or (at your
      14  option) any later version.
      15  
      16  The GNU MPFR Library is distributed in the hope that it will be useful, but
      17  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
      18  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
      19  License for more details.
      20  
      21  You should have received a copy of the GNU Lesser General Public License
      22  along with the GNU MPFR Library; see the file COPYING.LESSER.  If not, see
      23  https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
      24  51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
      25  
      26  
      27  #define MPFR_NEED_LONGLONG_H
      28  #include "mpfr-impl.h"
      29  
      30  /* generate nbits random bits into mp[], assuming mp was allocated to contain
      31     a sufficient number of limbs */
      32  void
      33  mpfr_rand_raw (mpfr_limb_ptr mp, gmp_randstate_t rstate,
      34                 mpfr_prec_t nbits)
      35  {
      36    mpz_t z;
      37  
      38    MPFR_ASSERTN (nbits >= 1);
      39    /* Check for integer overflow (unless mp_bitcnt_t is signed,
      40       but according to the GMP manual, this shouldn't happen).
      41       Note: mp_bitcnt_t has been introduced in GMP 5.0.0. */
      42    MPFR_ASSERTN ((mp_bitcnt_t) -1 < 0 || nbits <= (mp_bitcnt_t) -1);
      43    mpz_init (z);
      44    mpz_urandomb (z, rstate, nbits);
      45    MPN_COPY(mp, PTR(z), MPFR_PREC2LIMBS (nbits));
      46    mpz_clear (z);
      47  }
      48  
      49  int
      50  mpfr_urandomb (mpfr_ptr rop, gmp_randstate_t rstate)
      51  {
      52    mpfr_limb_ptr rp;
      53    mpfr_prec_t nbits;
      54    mp_size_t nlimbs;
      55    mp_size_t k; /* number of high zero limbs */
      56    mpfr_exp_t exp;
      57    int cnt;
      58  
      59    rp = MPFR_MANT (rop);
      60    nbits = MPFR_PREC (rop);
      61    nlimbs = MPFR_LIMB_SIZE (rop);
      62    MPFR_SET_POS (rop);
      63    cnt = nlimbs * GMP_NUMB_BITS - nbits;
      64  
      65    /* Uniform non-normalized significand */
      66    /* generate exactly nbits so that the random generator stays in the same
      67       state, independent of the machine word size GMP_NUMB_BITS */
      68    mpfr_rand_raw (rp, rstate, nbits);
      69    if (MPFR_LIKELY (cnt != 0)) /* this will put the low bits to zero */
      70      mpn_lshift (rp, rp, nlimbs, cnt);
      71  
      72    /* Count the null significant limbs and remaining limbs */
      73    exp = 0;
      74    k = 0;
      75    while (nlimbs != 0 && rp[nlimbs - 1] == 0)
      76      {
      77        k ++;
      78        nlimbs --;
      79        exp -= GMP_NUMB_BITS;
      80      }
      81  
      82    if (MPFR_LIKELY (nlimbs != 0)) /* otherwise value is zero */
      83      {
      84        count_leading_zeros (cnt, rp[nlimbs - 1]);
      85        /* Normalization */
      86        exp -= cnt;
      87        if (MPFR_UNLIKELY (! MPFR_EXP_IN_RANGE (exp)))
      88          {
      89            /* If the exponent is not in the current exponent range, we
      90               choose to return a NaN as this is probably a user error.
      91               Indeed this can happen only if the exponent range has been
      92               reduced to a very small interval and/or the precision is
      93               huge (very unlikely). */
      94            MPFR_SET_NAN (rop);
      95            __gmpfr_flags |= MPFR_FLAGS_NAN; /* Can't use MPFR_RET_NAN */
      96            return 1;
      97          }
      98        MPFR_SET_EXP (rop, exp);
      99        if (cnt != 0)
     100          mpn_lshift (rp + k, rp, nlimbs, cnt);
     101        else if (k != 0)
     102          mpn_copyd (rp + k, rp, nlimbs);
     103        if (k != 0)
     104          MPN_ZERO (rp, k);
     105      }
     106    else
     107      MPFR_SET_ZERO (rop);
     108  
     109    return 0;
     110  }