contrib/gmp/randbui.c

   1 /* gmp_urandomb_ui -- random bits returned in a ulong.
   2
   3 Copyright 2003, 2004 Free Software Foundation, Inc.
   4
   5 This file is part of the GNU MP Library.
   6
   7 The GNU MP Library is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU Lesser General Public License as published by
   9 the Free Software Foundation; either version 3 of the License, or (at your
  10 option) any later version.
  11
  12 The GNU MP Library is distributed in the hope that it will be useful, but
  13 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  14 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  15 License for more details.
  16
  17 You should have received a copy of the GNU Lesser General Public License
  18 along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
  19
  20 #include "gmp.h"
  21 #include "gmp-impl.h"
  22
  23
  24 /* Currently bits>=BITS_PER_ULONG is quietly truncated to BITS_PER_ULONG,
  25    maybe this should raise an exception or something.  */
  26
  27 unsigned long
  28 gmp_urandomb_ui (gmp_randstate_ptr rstate, unsigned long bits)
  29 {
  30   mp_limb_t  a[LIMBS_PER_ULONG];
  31
  32   /* start with zeros, since if bits==0 then _gmp_rand will store nothing at
  33      all, or if bits <= GMP_NUMB_BITS then it will store only a[0] */
  34   a[0] = 0;
  35 #if LIMBS_PER_ULONG > 1
  36   a[1] = 0;
  37 #endif
  38
  39   _gmp_rand (a, rstate, MIN (bits, BITS_PER_ULONG));
  40
  41 #if LIMBS_PER_ULONG == 1
  42   return a[0];
  43 #else
  44   return a[0] | (a[1] << GMP_NUMB_BITS);
  45 #endif
  46 }