/* 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 Free Software Foundation, Inc.

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., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA. */

#include "gmp.h"
#include "gmp-impl.h"
#include "longlong.h"
#include "mpfr.h"
#include "mpfr-impl.h"

void
mpfr_urandomb (mpfr_ptr rop, gmp_randstate_t rstate)
{
  mp_ptr rp;
  mp_prec_t nbits;
  mp_size_t nlimbs;
  mp_exp_t exp;
  int cnt;

  MPFR_CLEAR_FLAGS(rop);

  rp = MPFR_MANT(rop);
  nbits = MPFR_PREC(rop);
  nlimbs = (nbits + BITS_PER_MP_LIMB - 1) / BITS_PER_MP_LIMB;

  _gmp_rand (rp, rstate, nbits);

  /* If nbits isn't a multiple of BITS_PER_MP_LIMB, shift up.  */
  if (nbits % BITS_PER_MP_LIMB != 0)
    mpn_lshift (rp, rp, nlimbs, BITS_PER_MP_LIMB - nbits % BITS_PER_MP_LIMB);

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

  if (nlimbs != 0) /* otherwise value is zero */
    {
      count_leading_zeros (cnt, rp[nlimbs - 1]); 
      if (cnt != 0)
        mpn_lshift (rp, rp, nlimbs, cnt);
      exp -= cnt;

      cnt = (mp_prec_t) nlimbs * BITS_PER_MP_LIMB - nbits;
      /* cnt is the number of non significant bits in the low limb */
      rp[0] &= ~((MP_LIMB_T_ONE << cnt) - 1);
    }

  MPFR_EXP (rop) = exp;
  MPFR_SET_POS (rop);
}