randbui.c

/* gmp_urandomb_ui -- random bits returned in a ulong.

Copyright 2003, 2004 Free Software Foundation, Inc.

This file is part of the GNU MP Library.

The GNU MP 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 3 of the License, or (at your
option) any later version.

The GNU MP 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 GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */

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


/* Currently bits>=BITS_PER_ULONG is quietly truncated to BITS_PER_ULONG,
   maybe this should raise an exception or something.  */

unsigned long
gmp_urandomb_ui (gmp_randstate_ptr rstate, unsigned long bits)
{
  mp_limb_t  a[LIMBS_PER_ULONG];

  /* start with zeros, since if bits==0 then _gmp_rand will store nothing at
     all, or if bits <= GMP_NUMB_BITS then it will store only a[0] */
  a[0] = 0;
#if LIMBS_PER_ULONG > 1
  a[1] = 0;
#endif

  _gmp_rand (a, rstate, MIN (bits, BITS_PER_ULONG));

#if LIMBS_PER_ULONG == 1
  return a[0];
#else
  return a[0] | (a[1] << GMP_NUMB_BITS);
#endif
}