contrib/gmp/mpf/urandomb.c

   1 /* mpf_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().
   5
   6 Copyright 1999, 2000, 2001, 2002  Free Software Foundation, Inc.
   7
   8 This file is part of the GNU MP Library.
   9
  10 The GNU MP Library is free software; you can redistribute it and/or modify
  11 it under the terms of the GNU Lesser General Public License as published by
  12 the Free Software Foundation; either version 3 of the License, or (at your
  13 option) any later version.
  14
  15 The GNU MP Library is distributed in the hope that it will be useful, but
  16 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  17 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  18 License for more details.
  19
  20 You should have received a copy of the GNU Lesser General Public License
  21 along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
  22
  23 #include "gmp.h"
  24 #include "gmp-impl.h"
  25
  26 void
  27 mpf_urandomb (mpf_t rop, gmp_randstate_t rstate, mp_bitcnt_t nbits)
  28 {
  29   mp_ptr rp;
  30   mp_size_t nlimbs;
  31   mp_exp_t exp;
  32   mp_size_t prec;
  33
  34   rp = PTR (rop);
  35   nlimbs = BITS_TO_LIMBS (nbits);
  36   prec = PREC (rop);
  37
  38   if (nlimbs > prec + 1 || nlimbs == 0)
  39     {
  40       nlimbs = prec + 1;
  41       nbits = nlimbs * GMP_NUMB_BITS;
  42     }
  43
  44   _gmp_rand (rp, rstate, nbits);
  45
  46   /* If nbits isn't a multiple of GMP_NUMB_BITS, shift up.  */
  47   if (nbits % GMP_NUMB_BITS != 0)
  48     mpn_lshift (rp, rp, nlimbs, GMP_NUMB_BITS - nbits % GMP_NUMB_BITS);
  49
  50   exp = 0;
  51   while (nlimbs != 0 && rp[nlimbs - 1] == 0)
  52     {
  53       nlimbs--;
  54       exp--;
  55     }
  56   EXP (rop) = exp;
  57   SIZ (rop) = nlimbs;
  58 }