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/* mpfr_urandom (rop, state, rnd_mode) -- Generate a uniform pseudorandom
real number between 0 and 1 (exclusive) and round it to the precision of rop
according to the given rounding mode.
Copyright 2000-2004, 2006-2016 Free Software Foundation, Inc.
Contributed by the AriC and Caramel projects, INRIA.
This file is part of the GNU MPFR Library.
The GNU MPFR 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 MPFR 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 MPFR Library; see the file COPYING.LESSER. If not, see
http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
#define MPFR_NEED_LONGLONG_H
#include "mpfr-impl.h"
/* generate one random bit */
static int
random_rounding_bit (gmp_randstate_t rstate)
{
mp_limb_t r;
mpfr_rand_raw (&r, rstate, 1);
return r & MPFR_LIMB_ONE;
}
int
mpfr_urandom (mpfr_ptr rop, gmp_randstate_t rstate, mpfr_rnd_t rnd_mode)
{
mpfr_limb_ptr rp;
mpfr_prec_t nbits;
mp_size_t nlimbs;
mp_size_t n;
mpfr_exp_t exp;
mpfr_exp_t emin;
int cnt;
int inex;
rp = MPFR_MANT (rop);
nbits = MPFR_PREC (rop);
nlimbs = MPFR_LIMB_SIZE (rop);
MPFR_SET_POS (rop);
exp = 0;
emin = mpfr_get_emin ();
if (MPFR_UNLIKELY (emin > 0))
{
if (rnd_mode == MPFR_RNDU || rnd_mode == MPFR_RNDA
|| (emin == 1 && rnd_mode == MPFR_RNDN
&& random_rounding_bit (rstate)))
{
mpfr_set_ui_2exp (rop, 1, emin - 1, rnd_mode);
return +1;
}
else
{
MPFR_SET_ZERO (rop);
return -1;
}
}
/* Exponent */
#define DRAW_BITS 8 /* we draw DRAW_BITS at a time */
cnt = DRAW_BITS;
MPFR_ASSERTN(DRAW_BITS <= GMP_NUMB_BITS);
while (cnt == DRAW_BITS)
{
/* generate DRAW_BITS in rp[0] */
mpfr_rand_raw (rp, rstate, DRAW_BITS);
if (MPFR_UNLIKELY (rp[0] == 0))
cnt = DRAW_BITS;
else
{
count_leading_zeros (cnt, rp[0]);
cnt -= GMP_NUMB_BITS - DRAW_BITS;
}
if (MPFR_UNLIKELY (exp < emin + cnt))
{
/* To get here, we have been drawing more than -emin zeros
in a row, then return 0 or the smallest representable
positive number.
The rounding to nearest mode is subtle:
If exp - cnt == emin - 1, the rounding bit is set, except
if cnt == DRAW_BITS in which case the rounding bit is
outside rp[0] and must be generated. */
if (rnd_mode == MPFR_RNDU || rnd_mode == MPFR_RNDA
|| (rnd_mode == MPFR_RNDN && cnt == exp - emin - 1
&& (cnt != DRAW_BITS || random_rounding_bit (rstate))))
{
mpfr_set_ui_2exp (rop, 1, emin - 1, rnd_mode);
return +1;
}
else
{
MPFR_SET_ZERO (rop);
return -1;
}
}
exp -= cnt;
}
MPFR_EXP (rop) = exp; /* Warning: may be outside the current
exponent range */
/* Significand: we need generate only nbits-1 bits, since the most
significant is 1 */
mpfr_rand_raw (rp, rstate, nbits - 1);
n = nlimbs * GMP_NUMB_BITS - nbits;
if (MPFR_LIKELY (n != 0)) /* this will put the low bits to zero */
mpn_lshift (rp, rp, nlimbs, n);
/* Set the msb to 1 since it was fixed by the exponent choice */
rp[nlimbs - 1] |= MPFR_LIMB_HIGHBIT;
/* Rounding */
if (rnd_mode == MPFR_RNDU || rnd_mode == MPFR_RNDA
|| (rnd_mode == MPFR_RNDN && random_rounding_bit (rstate)))
{
/* Take care of the exponent range: it may have been reduced */
if (exp < emin)
mpfr_set_ui_2exp (rop, 1, emin - 1, rnd_mode);
else if (exp > mpfr_get_emax ())
mpfr_set_inf (rop, +1); /* overflow, flag set by mpfr_check_range */
else
mpfr_nextabove (rop);
inex = +1;
}
else
inex = -1;
return mpfr_check_range (rop, inex, rnd_mode);
}
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