/* mpc_sqr -- Square a complex number.
Copyright (C) 2002, 2005, 2008, 2009, 2010, 2011, 2012 INRIA
This file is part of GNU MPC.
GNU MPC 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.
GNU MPC 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 this program. If not, see http://www.gnu.org/licenses/ .
*/
#include <stdio.h> /* for MPC_ASSERT */
#include "mpc-impl.h"
static int
mpfr_fsss (mpfr_ptr z, mpfr_srcptr a, mpfr_srcptr c, mpfr_rnd_t rnd)
{
/* Computes z = a^2 - c^2.
Assumes that a and c are finite and non-zero; so a squaring yielding
an infinity is an overflow, and a squaring yielding 0 is an underflow.
Assumes further that z is distinct from a and c. */
int inex;
mpfr_t u, v;
/* u=a^2, v=c^2 exactly */
mpfr_init2 (u, 2*mpfr_get_prec (a));
mpfr_init2 (v, 2*mpfr_get_prec (c));
mpfr_sqr (u, a, MPFR_RNDN);
mpfr_sqr (v, c, MPFR_RNDN);
/* tentatively compute z as u-v; here we need z to be distinct
from a and c to not lose the latter */
inex = mpfr_sub (z, u, v, rnd);
if (mpfr_inf_p (z)) {
/* replace by "correctly rounded overflow" */
mpfr_set_si (z, (mpfr_signbit (z) ? -1 : 1), MPFR_RNDN);
inex = mpfr_mul_2ui (z, z, mpfr_get_emax (), rnd);
}
else if (mpfr_zero_p (u) && !mpfr_zero_p (v)) {
/* exactly u underflowed, determine inexact flag */
inex = (mpfr_signbit (u) ? 1 : -1);
}
else if (mpfr_zero_p (v) && !mpfr_zero_p (u)) {
/* exactly v underflowed, determine inexact flag */
inex = (mpfr_signbit (v) ? -1 : 1);
}
else if (mpfr_nan_p (z) || (mpfr_zero_p (u) && mpfr_zero_p (v))) {
/* In the first case, u and v are +inf.
In the second case, u and v are zeroes; their difference may be 0
or the least representable number, with a sign to be determined.
Redo the computations with mpz_t exponents */
mpfr_exp_t ea, ec;
mpz_t eu, ev;
/* cheat to work around the const qualifiers */
/* Normalise the input by shifting and keep track of the shifts in
the exponents of u and v */
ea = mpfr_get_exp (a);
ec = mpfr_get_exp (c);
mpfr_set_exp ((mpfr_ptr) a, (mpfr_prec_t) 0);
mpfr_set_exp ((mpfr_ptr) c, (mpfr_prec_t) 0);
mpz_init (eu);
mpz_init (ev);
mpz_set_si (eu, (long int) ea);
mpz_mul_2exp (eu, eu, 1);
mpz_set_si (ev, (long int) ec);
mpz_mul_2exp (ev, ev, 1);
/* recompute u and v and move exponents to eu and ev */
mpfr_sqr (u, a, MPFR_RNDN);
/* exponent of u is non-positive */
mpz_sub_ui (eu, eu, (unsigned long int) (-mpfr_get_exp (u)));
mpfr_set_exp (u, (mpfr_prec_t) 0);
mpfr_sqr (v, c, MPFR_RNDN);
mpz_sub_ui (ev, ev, (unsigned long int) (-mpfr_get_exp (v)));
mpfr_set_exp (v, (mpfr_prec_t) 0);
if (mpfr_nan_p (z)) {
mpfr_exp_t emax = mpfr_get_emax ();
int overflow;
/* We have a = ma * 2^ea with 1/2 <= |ma| < 1 and ea <= emax.
So eu <= 2*emax, and eu > emax since we have
an overflow. The same holds for ev. Shift u and v by as much as
possible so that one of them has exponent emax and the
remaining exponents in eu and ev are the same. Then carry out
the addition. Shifting u and v prevents an underflow. */
if (mpz_cmp (eu, ev) >= 0) {
mpfr_set_exp (u, emax);
mpz_sub_ui (eu, eu, (long int) emax);
mpz_sub (ev, ev, eu);
mpfr_set_exp (v, (mpfr_exp_t) mpz_get_ui (ev));
/* remaining common exponent is now in eu */
}
else {
mpfr_set_exp (v, emax);
mpz_sub_ui (ev, ev, (long int) emax);
mpz_sub (eu, eu, ev);
mpfr_set_exp (u, (mpfr_exp_t) mpz_get_ui (eu));
mpz_set (eu, ev);
/* remaining common exponent is now also in eu */
}
inex = mpfr_sub (z, u, v, rnd);
/* Result is finite since u and v have the same sign. */
overflow = mpfr_mul_2ui (z, z, mpz_get_ui (eu), rnd);
if (overflow)
inex = overflow;
}
else {
int underflow;
/* Subtraction of two zeroes. We have a = ma * 2^ea
with 1/2 <= |ma| < 1 and ea >= emin and similarly for b.
So 2*emin < 2*emin+1 <= eu < emin < 0, and analogously for v. */
mpfr_exp_t emin = mpfr_get_emin ();
if (mpz_cmp (eu, ev) <= 0) {
mpfr_set_exp (u, emin);
mpz_add_ui (eu, eu, (unsigned long int) (-emin));
mpz_sub (ev, ev, eu);
mpfr_set_exp (v, (mpfr_exp_t) mpz_get_si (ev));
}
else {
mpfr_set_exp (v, emin);
mpz_add_ui (ev, ev, (unsigned long int) (-emin));
mpz_sub (eu, eu, ev);
mpfr_set_exp (u, (mpfr_exp_t) mpz_get_si (eu));
mpz_set (eu, ev);
}
inex = mpfr_sub (z, u, v, rnd);
mpz_neg (eu, eu);
underflow = mpfr_div_2ui (z, z, mpz_get_ui (eu), rnd);
if (underflow)
inex = underflow;
}
mpz_clear (eu);
mpz_clear (ev);
mpfr_set_exp ((mpfr_ptr) a, ea);
mpfr_set_exp ((mpfr_ptr) c, ec);
/* works also when a == c */
}
mpfr_clear (u);
mpfr_clear (v);
return inex;
}
int
mpc_sqr (mpc_ptr rop, mpc_srcptr op, mpc_rnd_t rnd)
{
int ok;
mpfr_t u, v;
mpfr_t x;
/* temporary variable to hold the real part of op,
needed in the case rop==op */
mpfr_prec_t prec;
int inex_re, inex_im, inexact;
mpfr_exp_t emin;
int saved_underflow;
/* special values: NaN and infinities */
if (!mpc_fin_p (op)) {
if (mpfr_nan_p (mpc_realref (op)) || mpfr_nan_p (mpc_imagref (op))) {
mpfr_set_nan (mpc_realref (rop));
mpfr_set_nan (mpc_imagref (rop));
}
else if (mpfr_inf_p (mpc_realref (op))) {
if (mpfr_inf_p (mpc_imagref (op))) {
mpfr_set_inf (mpc_imagref (rop),
MPFR_SIGN (mpc_realref (op)) * MPFR_SIGN (mpc_imagref (op)));
mpfr_set_nan (mpc_realref (rop));
}
else {
if (mpfr_zero_p (mpc_imagref (op)))
mpfr_set_nan (mpc_imagref (rop));
else
mpfr_set_inf (mpc_imagref (rop),
MPFR_SIGN (mpc_realref (op)) * MPFR_SIGN (mpc_imagref (op)));
mpfr_set_inf (mpc_realref (rop), +1);
}
}
else /* IM(op) is infinity, RE(op) is not */ {
if (mpfr_zero_p (mpc_realref (op)))
mpfr_set_nan (mpc_imagref (rop));
else
mpfr_set_inf (mpc_imagref (rop),
MPFR_SIGN (mpc_realref (op)) * MPFR_SIGN (mpc_imagref (op)));
mpfr_set_inf (mpc_realref (rop), -1);
}
return MPC_INEX (0, 0); /* exact */
}
prec = MPC_MAX_PREC(rop);
/* Check for real resp. purely imaginary number */
if (mpfr_zero_p (mpc_imagref(op))) {
int same_sign = mpfr_signbit (mpc_realref (op)) == mpfr_signbit (mpc_imagref (op));
inex_re = mpfr_sqr (mpc_realref(rop), mpc_realref(op), MPC_RND_RE(rnd));
inex_im = mpfr_set_ui (mpc_imagref(rop), 0ul, MPFR_RNDN);
if (!same_sign)
mpc_conj (rop, rop, MPC_RNDNN);
return MPC_INEX(inex_re, inex_im);
}
if (mpfr_zero_p (mpc_realref(op))) {
int same_sign = mpfr_signbit (mpc_realref (op)) == mpfr_signbit (mpc_imagref (op));
inex_re = -mpfr_sqr (mpc_realref(rop), mpc_imagref(op), INV_RND (MPC_RND_RE(rnd)));
mpfr_neg (mpc_realref(rop), mpc_realref(rop), MPFR_RNDN);
inex_im = mpfr_set_ui (mpc_imagref(rop), 0ul, MPFR_RNDN);
if (!same_sign)
mpc_conj (rop, rop, MPC_RNDNN);
return MPC_INEX(inex_re, inex_im);
}
if (rop == op)
{
mpfr_init2 (x, MPC_PREC_RE (op));
mpfr_set (x, op->re, MPFR_RNDN);
}
else
x [0] = op->re [0];
/* From here on, use x instead of op->re and safely overwrite rop->re. */
/* Compute real part of result. */
if (SAFE_ABS (mpfr_exp_t,
mpfr_get_exp (mpc_realref (op)) - mpfr_get_exp (mpc_imagref (op)))
> (mpfr_exp_t) MPC_MAX_PREC (op) / 2) {
/* If the real and imaginary parts of the argument have very different
exponents, it is not reasonable to use Karatsuba squaring; compute
exactly with the standard formulae instead, even if this means an
additional multiplication. Using the approach copied from mul, over-
and underflows are also handled correctly. */
inex_re = mpfr_fsss (rop->re, x, op->im, MPC_RND_RE (rnd));
}
else {
/* Karatsuba squaring: we compute the real part as (x+y)*(x-y) and the
imaginary part as 2*x*y, with a total of 2M instead of 2S+1M for the
naive algorithm, which computes x^2-y^2 and 2*y*y */
mpfr_init (u);
mpfr_init (v);
emin = mpfr_get_emin ();
do
{
prec += mpc_ceil_log2 (prec) + 5;
mpfr_set_prec (u, prec);
mpfr_set_prec (v, prec);
/* Let op = x + iy. We need u = x+y and v = x-y, rounded away. */
/* The error is bounded above by 1 ulp. */
/* We first let inexact be 1 if the real part is not computed */
/* exactly and determine the sign later. */
inexact = mpfr_add (u, x, mpc_imagref (op), MPFR_RNDA)
| mpfr_sub (v, x, mpc_imagref (op), MPFR_RNDA);
/* compute the real part as u*v, rounded away */
/* determine also the sign of inex_re */
if (mpfr_sgn (u) == 0 || mpfr_sgn (v) == 0) {
/* as we have rounded away, the result is exact */
mpfr_set_ui (mpc_realref (rop), 0, MPFR_RNDN);
inex_re = 0;
ok = 1;
}
else {
inexact |= mpfr_mul (u, u, v, MPFR_RNDA); /* error 5 */
if (mpfr_get_exp (u) == emin || mpfr_inf_p (u)) {
/* under- or overflow */
inex_re = mpfr_fsss (rop->re, x, op->im, MPC_RND_RE (rnd));
ok = 1;
}
else {
ok = (!inexact) | mpfr_can_round (u, prec - 3,
MPFR_RNDA, MPFR_RNDZ,
MPC_PREC_RE (rop) + (MPC_RND_RE (rnd) == MPFR_RNDN));
if (ok) {
inex_re = mpfr_set (mpc_realref (rop), u, MPC_RND_RE (rnd));
if (inex_re == 0)
/* remember that u was already rounded */
inex_re = inexact;
}
}
}
}
while (!ok);
mpfr_clear (u);
mpfr_clear (v);
}
saved_underflow = mpfr_underflow_p ();
mpfr_clear_underflow ();
inex_im = mpfr_mul (rop->im, x, op->im, MPC_RND_IM (rnd));
if (!mpfr_underflow_p ())
inex_im |= mpfr_mul_2ui (rop->im, rop->im, 1, MPC_RND_IM (rnd));
/* We must not multiply by 2 if rop->im has been set to the smallest
representable number. */
if (saved_underflow)
mpfr_set_underflow ();
if (rop == op)
mpfr_clear (x);
return MPC_INEX (inex_re, inex_im);
}