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/* mpz_urandomm (rop, state, n) -- Generate a uniform pseudorandom
integer in the range 0 to N-1, using STATE as the random state
previously initialized by a call to gmp_randinit().
Copyright (C) 2000 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 Library General Public License as published by
the Free Software Foundation; either version 2 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 Library General Public
License for more details.
You should have received a copy of the GNU Library General Public License
along with the GNU MP 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"
void
#if __STDC__
mpz_urandomm (mpz_t rop, gmp_randstate_t rstate, mpz_t n)
#else
mpz_urandomm (rop, rstate, n)
mpz_t rop;
gmp_randstate_t rstate;
mpz_t n;
#endif
{
mpz_t t, p, m;
mp_ptr tp;
mp_size_t nbits, size;
int count;
/* FIXME: Should check for n == 0 and report error */
size = SIZ (n);
count_leading_zeros (count, PTR (n)[size - 1]);
nbits = size * BITS_PER_MP_LIMB - count;
/* Allocate enough for any mpz function called since a realloc of
these will fail. */
MPZ_TMP_INIT (t, size);
MPZ_TMP_INIT (m, size + 1);
MPZ_TMP_INIT (p, size + 1);
/* Let m = highest possible random number plus 1. */
mpz_set_ui (m, 0);
mpz_setbit (m, nbits);
/* Let p = floor(m / n) * n. */
mpz_fdiv_q (p, m, n);
mpz_mul (p, p, n);
tp = PTR (t);
do
{
_gmp_rand (tp, rstate, nbits);
MPN_NORMALIZE (tp, size); /* FIXME: Really necessary? */
SIZ (t) = size;
}
while (mpz_cmp (t, p) >= 0);
mpz_mod (rop, t, n);
}
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