SEXP R_mpfr_get_erange(SEXP kind_) {
erange_kind kind = asInteger(kind_);
/* MUST be sync'ed with ../R/mpfr.R
* ~~~~~~~~~~~ where .Summary.codes <-
*/
mpfr_exp_t r;
switch(kind) {
case E_min: r = mpfr_get_emin(); break;
case E_max: r = mpfr_get_emax(); break;
case min_emin: r = mpfr_get_emin_min(); break;
case max_emin: r = mpfr_get_emin_max(); break;
case min_emax: r = mpfr_get_emax_min(); break;
case max_emax: r = mpfr_get_emax_max(); break;
default:
error("invalid kind (code = %d) in R_mpfr_get_erange()", kind);
}
R_mpfr_dbg_printf(1,"R_mpfr_get_erange(%d): %ld\n", kind, (long)r);
return (kind <= E_max && INT_MIN <= r && r <= INT_MAX) ? ScalarInteger((int) r)
: ScalarReal((double) r);
}
/* If x^y is exactly representable (with maybe a larger precision than z),
round it in z and return the (mpc) inexact flag in [0, 10].
If x^y is not exactly representable, return -1.
If intermediate computations lead to numbers of more than maxprec bits,
then abort and return -2 (in that case, to avoid loops, mpc_pow_exact
should be called again with a larger value of maxprec).
Assume one of Re(x) or Im(x) is non-zero, and y is non-zero (y is real).
*/
static int
mpc_pow_exact (mpc_ptr z, mpc_srcptr x, mpfr_srcptr y, mpc_rnd_t rnd,
mp_prec_t maxprec)
{
mp_exp_t ec, ed, ey, emin, emax;
mpz_t my, a, b, c, d, u;
unsigned long int t;
int ret = -2;
mpz_init (my);
mpz_init (a);
mpz_init (b);
mpz_init (c);
mpz_init (d);
mpz_init (u);
ey = mpfr_get_z_exp (my, y);
/* normalize so that my is odd */
t = mpz_scan1 (my, 0);
ey += t;
mpz_tdiv_q_2exp (my, my, t);
if (mpfr_zero_p (MPC_RE(x)))
{
mpz_set_ui (c, 0);
ec = 0;
}
else
ec = mpfr_get_z_exp (c, MPC_RE(x));
if (mpfr_zero_p (MPC_IM(x)))
{
mpz_set_ui (d, 0);
ed = ec;
}
else
{
ed = mpfr_get_z_exp (d, MPC_IM(x));
if (mpfr_zero_p (MPC_RE(x)))
ec = ed;
}
/* x = c*2^ec + I * d*2^ed */
/* equalize the exponents of x */
if (ec < ed)
{
mpz_mul_2exp (d, d, ed - ec);
if (mpz_sizeinbase (d, 2) > maxprec)
goto end;
ed = ec;
}
else if (ed < ec)
{
mpz_mul_2exp (c, c, ec - ed);
if (mpz_sizeinbase (c, 2) > maxprec)
goto end;
ec = ed;
}
/* now ec=ed and x = (c + I * d) * 2^ec */
/* divide by two if possible */
if (mpz_cmp_ui (c, 0) == 0)
{
t = mpz_scan1 (d, 0);
mpz_tdiv_q_2exp (d, d, t);
ec += t;
}
else if (mpz_cmp_ui (d, 0) == 0)
{
t = mpz_scan1 (c, 0);
mpz_tdiv_q_2exp (c, c, t);
ec += t;
}
else /* neither c nor d is zero */
{
unsigned long v;
t = mpz_scan1 (c, 0);
v = mpz_scan1 (d, 0);
if (v < t)
t = v;
mpz_tdiv_q_2exp (c, c, t);
mpz_tdiv_q_2exp (d, d, t);
ec += t;
}
/* now either one of c, d is odd */
while (ey < 0)
{
/* check if x is a square */
if (ec & 1)
{
mpz_mul_2exp (c, c, 1);
mpz_mul_2exp (d, d, 1);
ec --;
}
/* now ec is even */
if (mpc_perfect_square_p (a, b, c, d) == 0)
break;
mpz_swap (a, c);
mpz_swap (b, d);
ec /= 2;
ey ++;
}
if (ey < 0)
{
ret = -1; /* not representable */
goto end;
}
/* Now ey >= 0, it thus suffices to check that x^my is representable.
If my > 0, this is always true. If my < 0, we first try to invert
(c+I*d)*2^ec.
*/
if (mpz_cmp_ui (my, 0) < 0)
{
/* If my < 0, 1 / (c + I*d) = (c - I*d)/(c^2 + d^2), thus a sufficient
condition is that c^2 + d^2 is a power of two, assuming |c| <> |d|.
Assume a prime p <> 2 divides c^2 + d^2,
then if p does not divide c or d, 1 / (c + I*d) cannot be exact.
If p divides both c and d, then we can write c = p*c', d = p*d',
and 1 / (c + I*d) = 1/p * 1/(c' + I*d'). This shows that if 1/(c+I*d)
is exact, then 1/(c' + I*d') is exact too, and we are back to the
previous case. In conclusion, a necessary and sufficient condition
is that c^2 + d^2 is a power of two.
*/
/* FIXME: we could first compute c^2+d^2 mod a limb for example */
mpz_mul (a, c, c);
mpz_addmul (a, d, d);
t = mpz_scan1 (a, 0);
if (mpz_sizeinbase (a, 2) != 1 + t) /* a is not a power of two */
{
ret = -1; /* not representable */
goto end;
}
/* replace (c,d) by (c/(c^2+d^2), -d/(c^2+d^2)) */
mpz_neg (d, d);
ec = -ec - t;
mpz_neg (my, my);
}
/* now ey >= 0 and my >= 0, and we want to compute
[(c + I * d) * 2^ec] ^ (my * 2^ey).
We first compute [(c + I * d) * 2^ec]^my, then square ey times. */
t = mpz_sizeinbase (my, 2) - 1;
mpz_set (a, c);
mpz_set (b, d);
ed = ec;
/* invariant: (a + I*b) * 2^ed = ((c + I*d) * 2^ec)^trunc(my/2^t) */
while (t-- > 0)
{
unsigned long v, w;
/* square a + I*b */
mpz_mul (u, a, b);
mpz_mul (a, a, a);
mpz_submul (a, b, b);
mpz_mul_2exp (b, u, 1);
ed *= 2;
if (mpz_tstbit (my, t)) /* multiply by c + I*d */
{
mpz_mul (u, a, c);
mpz_submul (u, b, d); /* ac-bd */
mpz_mul (b, b, c);
mpz_addmul (b, a, d); /* bc+ad */
mpz_swap (a, u);
ed += ec;
}
/* remove powers of two in (a,b) */
if (mpz_cmp_ui (a, 0) == 0)
{
w = mpz_scan1 (b, 0);
mpz_tdiv_q_2exp (b, b, w);
ed += w;
}
else if (mpz_cmp_ui (b, 0) == 0)
{
w = mpz_scan1 (a, 0);
mpz_tdiv_q_2exp (a, a, w);
ed += w;
}
else
{
w = mpz_scan1 (a, 0);
v = mpz_scan1 (b, 0);
if (v < w)
w = v;
mpz_tdiv_q_2exp (a, a, w);
mpz_tdiv_q_2exp (b, b, w);
ed += w;
}
if (mpz_sizeinbase (a, 2) > maxprec || mpz_sizeinbase (b, 2) > maxprec)
goto end;
}
/* now a+I*b = (c+I*d)^my */
while (ey-- > 0)
{
unsigned long sa, sb;
/* square a + I*b */
mpz_mul (u, a, b);
mpz_mul (a, a, a);
mpz_submul (a, b, b);
mpz_mul_2exp (b, u, 1);
ed *= 2;
/* divide by largest 2^n possible, to avoid many loops for e.g.,
(2+2*I)^16777216 */
sa = mpz_scan1 (a, 0);
sb = mpz_scan1 (b, 0);
sa = (sa <= sb) ? sa : sb;
mpz_tdiv_q_2exp (a, a, sa);
mpz_tdiv_q_2exp (b, b, sa);
ed += sa;
if (mpz_sizeinbase (a, 2) > maxprec || mpz_sizeinbase (b, 2) > maxprec)
goto end;
}
/* save emin, emax */
emin = mpfr_get_emin ();
emax = mpfr_get_emax ();
mpfr_set_emin (mpfr_get_emin_min ());
mpfr_set_emax (mpfr_get_emax_max ());
ret = mpfr_set_z (MPC_RE(z), a, MPC_RND_RE(rnd));
ret = MPC_INEX(ret, mpfr_set_z (MPC_IM(z), b, MPC_RND_IM(rnd)));
mpfr_mul_2si (MPC_RE(z), MPC_RE(z), ed, MPC_RND_RE(rnd));
mpfr_mul_2si (MPC_IM(z), MPC_IM(z), ed, MPC_RND_IM(rnd));
/* restore emin, emax */
mpfr_set_emin (emin);
mpfr_set_emax (emax);
end:
mpz_clear (my);
mpz_clear (a);
mpz_clear (b);
mpz_clear (c);
mpz_clear (d);
mpz_clear (u);
return ret;
}
