/* mpfr_urandomb (rop, state, nbits) -- Generate a uniform pseudorandom
   real number between 0 (inclusive) and 1 (exclusive) of size NBITS,
   using STATE as the random state previously initialized by a call to
   gmp_randinit().

Copyright 2000, 2001, 2002, 2003, 2004, 2006, 2007 Free Software Foundation, Inc.
Contributed by the Arenaire and Cacao projects, INRIA.

This file is part of the MPFR Library.

The MPFR Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or (at your
option) any later version.

The MPFR Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
License for more details.

You should have received a copy of the GNU Lesser General Public License
along with the MPFR Library; see the file COPYING.LIB.  If not, write to
the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
MA 02110-1301, USA. */


#define MPFR_NEED_LONGLONG_H
#include "mpfr-impl.h"

int
mpfr_urandomb (mpfr_ptr rop, gmp_randstate_t rstate)
{
  mp_ptr rp;
  mp_prec_t nbits;
  mp_size_t nlimbs;
  mp_size_t k; /* number of high zero limbs */
  mp_exp_t exp;
  int cnt;

  MPFR_CLEAR_FLAGS(rop);

  rp = MPFR_MANT(rop);
  nbits = MPFR_PREC(rop);
  nlimbs = MPFR_LIMB_SIZE(rop);
  MPFR_SET_POS (rop);

  _gmp_rand (rp, rstate, nlimbs * BITS_PER_MP_LIMB);

  /* If nbits isn't a multiple of BITS_PER_MP_LIMB, mask the low bits */
  cnt = nlimbs * BITS_PER_MP_LIMB - nbits;
  if (MPFR_LIKELY(cnt != 0))
    rp[0] &= ~MPFR_LIMB_MASK (cnt);

  exp = 0;
  k = 0;
  while (nlimbs != 0 && rp[nlimbs - 1] == 0)
    {
      k ++;
      nlimbs --;
      exp -= BITS_PER_MP_LIMB;
    }

  if (MPFR_LIKELY(nlimbs != 0)) /* otherwise value is zero */
    {
      count_leading_zeros (cnt, rp[nlimbs - 1]);
      if (mpfr_set_exp (rop, exp - cnt))
        {
          MPFR_SET_NAN (rop);
          __gmpfr_flags |= MPFR_FLAGS_NAN; /* Can't use MPFR_RET_NAN */
          return 1;
        }
      if (cnt != 0)
        mpn_lshift (rp + k, rp, nlimbs, cnt);
      if (k)
        MPN_ZERO (rp, k);
    }
  else
    MPFR_SET_ZERO(rop);

  return 0;
}