/* generate a random limb */
mp_limb_t
randlimb (void)
{
mp_limb_t limb;
mpfr_rand_raw (&limb, RANDS, GMP_NUMB_BITS);
return limb;
}
/* 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_urandomb (mpfr_ptr rop, gmp_randstate_t rstate)
{
mpfr_limb_ptr rp;
mpfr_prec_t nbits;
mp_size_t nlimbs;
mp_size_t k; /* number of high zero limbs */
mpfr_exp_t exp;
int cnt;
rp = MPFR_MANT (rop);
nbits = MPFR_PREC (rop);
nlimbs = MPFR_LIMB_SIZE (rop);
MPFR_SET_POS (rop);
cnt = nlimbs * GMP_NUMB_BITS - nbits;
/* Uniform non-normalized significand */
/* generate exactly nbits so that the random generator stays in the same
state, independent of the machine word size GMP_NUMB_BITS */
mpfr_rand_raw (rp, rstate, nbits);
if (MPFR_LIKELY (cnt != 0)) /* this will put the low bits to zero */
mpn_lshift (rp, rp, nlimbs, cnt);
/* Count the null significant limbs and remaining limbs */
exp = 0;
k = 0;
while (nlimbs != 0 && rp[nlimbs - 1] == 0)
{
k ++;
nlimbs --;
exp -= GMP_NUMB_BITS;
}
if (MPFR_LIKELY (nlimbs != 0)) /* otherwise value is zero */
{
count_leading_zeros (cnt, rp[nlimbs - 1]);
/* Normalization */
if (mpfr_set_exp (rop, exp - cnt))
{
/* If the exponent is not in the current exponent range, we
choose to return a NaN as this is probably a user error.
Indeed this can happen only if the exponent range has been
reduced to a very small interval and/or the precision is
huge (very unlikely). */
MPFR_SET_NAN (rop);
__gmpfr_flags |= MPFR_FLAGS_NAN; /* Can't use MPFR_RET_NAN */
return 1;
}
if (cnt != 0)
mpn_lshift (rp + k, rp, nlimbs, cnt);
if (k != 0)
MPN_ZERO (rp, k);
}
else
MPFR_SET_ZERO (rop);
return 0;
}
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);
}
