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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 2000, 2002 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"
#include "longlong.h" /* for count_leading_zeros */
#define MAX_URANDOMM_ITER 80
void
mpz_urandomm (mpz_ptr rop, gmp_randstate_t rstate, mpz_srcptr n)
{
mp_ptr rp, np, nlast;
mp_size_t nbits, size;
int count;
int pow2;
int cmp;
TMP_DECL;
size = ABSIZ (n);
if (size == 0)
DIVIDE_BY_ZERO;
nlast = &PTR (n)[size - 1];
/* Detect whether n is a power of 2. */
pow2 = POW2_P (*nlast);
if (pow2 != 0)
for (np = PTR (n); np < nlast; np++)
if (*np != 0)
{
pow2 = 0; /* Mark n as `not a power of two'. */
break;
}
count_leading_zeros (count, *nlast);
nbits = size * GMP_NUMB_BITS - (count - GMP_NAIL_BITS) - pow2;
if (nbits == 0) /* nbits == 0 means that n was == 1. */
{
SIZ (rop) = 0;
return;
}
TMP_MARK;
np = PTR (n);
if (rop == n)
{
mp_ptr tp;
tp = TMP_ALLOC_LIMBS (size);
MPN_COPY (tp, np, size);
np = tp;
}
/* Here the allocated size can be one too much if n is a power of
(2^GMP_NUMB_BITS) but it's convenient for using mpn_cmp below. */
rp = MPZ_REALLOC (rop, size);
/* Clear last limb to prevent the case in which size is one too much. */
rp[size - 1] = 0;
count = MAX_URANDOMM_ITER; /* Set iteration count limit. */
do
{
_gmp_rand (rp, rstate, nbits);
MPN_CMP (cmp, rp, np, size);
}
while (cmp >= 0 && --count != 0);
if (count == 0)
/* Too many iterations; return result mod n == result - n */
mpn_sub_n (rp, rp, np, size);
MPN_NORMALIZE (rp, size);
SIZ (rop) = size;
TMP_FREE;
}
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