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/* mpfr_random2 -- Generate a positive random mpfr_t of specified size, with
long runs of consecutive ones and zeros in the binary representation.
Copyright 1999, 2001-2004, 2006-2020 Free Software Foundation, Inc.
Contributed by the AriC and Caramba 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
https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
#include "mpfr-test.h"
#if GMP_NUMB_BITS < 16
#define LOGBITS_PER_BLOCK 3
#else
#define LOGBITS_PER_BLOCK 4
#endif
#if GMP_NUMB_BITS < 32
#define BITS_PER_RANDCALL GMP_NUMB_BITS
#else
#define BITS_PER_RANDCALL 32
#endif
/* exp is the maximum exponent in absolute value */
void
mpfr_random2 (mpfr_ptr x, mp_size_t size, mpfr_exp_t exp,
gmp_randstate_t rstate)
{
mp_size_t xn, k, ri;
unsigned long sh;
mp_limb_t *xp;
mp_limb_t elimb, ran, acc;
int ran_nbits, bit_pos, nb;
if (MPFR_UNLIKELY(size == 0))
{
MPFR_SET_ZERO (x);
MPFR_SET_POS (x);
return ;
}
else if (size > 0)
{
MPFR_SET_POS (x);
}
else
{
MPFR_SET_NEG (x);
size = -size;
}
xn = MPFR_LIMB_SIZE (x);
xp = MPFR_MANT (x);
if (size > xn)
size = xn;
k = xn - size;
/* Code extracted from GMP, function mpn_random2, to avoid the use
of GMP's internal random state in MPFR */
mpfr_rand_raw (&elimb, rstate, BITS_PER_RANDCALL);
ran = elimb;
/* Start off at a random bit position in the most significant limb. */
bit_pos = GMP_NUMB_BITS - 1;
ran >>= MPFR_LOG2_GMP_NUMB_BITS; /* Ideally log2(GMP_NUMB_BITS) */
ran_nbits = BITS_PER_RANDCALL - MPFR_LOG2_GMP_NUMB_BITS; /* Ideally - log2(GMP_NUMB_BITS) */
/* Bit 0 of ran chooses string of ones/string of zeroes.
Make most significant limb be non-zero by setting bit 0 of RAN. */
ran |= 1;
ri = xn - 1;
acc = 0;
while (ri >= k)
{
if (ran_nbits < LOGBITS_PER_BLOCK + 1)
{
mpfr_rand_raw (&elimb, rstate, BITS_PER_RANDCALL);
ran = elimb;
ran_nbits = BITS_PER_RANDCALL;
}
nb = (ran >> 1) % (1 << LOGBITS_PER_BLOCK) + 1;
if ((ran & 1) != 0)
{
MPFR_ASSERTN (bit_pos < GMP_NUMB_BITS);
/* Generate a string of nb ones. */
if (nb > bit_pos)
{
xp[ri--] = acc | MPFR_LIMB_MASK (bit_pos + 1);
bit_pos += GMP_NUMB_BITS;
bit_pos -= nb;
acc = MPFR_LIMB_LSHIFT (MPFR_LIMB_MAX << 1, bit_pos);
}
else
{
bit_pos -= nb;
acc |= MPFR_LIMB_LSHIFT (MPFR_LIMB_MASK (nb) << 1, bit_pos);
}
}
else
{
/* Generate a string of nb zeroes. */
if (nb > bit_pos)
{
xp[ri--] = acc;
acc = 0;
bit_pos += GMP_NUMB_BITS;
}
bit_pos -= nb;
}
ran_nbits -= LOGBITS_PER_BLOCK + 1;
ran >>= LOGBITS_PER_BLOCK + 1;
}
/* Set mandatory most significant bit. */
/* xp[xn - 1] |= MPFR_LIMB_HIGHBIT; */
if (k != 0)
{
/* Clear last limbs */
MPN_ZERO (xp, k);
}
else
{
/* Mask off non significant bits in the low limb. */
MPFR_UNSIGNED_MINUS_MODULO (sh, MPFR_PREC (x));
xp[0] &= ~MPFR_LIMB_MASK (sh);
}
/* Generate random exponent. */
mpfr_rand_raw (&elimb, RANDS, GMP_NUMB_BITS);
MPFR_ASSERTN (exp >= 0 && exp <= MPFR_EMAX_MAX);
exp = (mpfr_exp_t) (elimb % (2 * exp + 1)) - exp;
MPFR_SET_EXP (x, exp);
return ;
}
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