Ejemplo n.º 1
0
int PXtoLong(unsigned long long number, unsigned long long *ret, int type) {
	unsigned long long retval = 0;
	char *s = (char *)&number;
	char *d = (char *)&retval;

	switch (type) {
		case PX_Field_Type_Logical:
			copy_from_be(d,s,1);

			if (s[0] & 0x80) {
				fix_sign(d, 1);
			} else if (retval == 0) {
				return VALUE_IS_NULL;
			} else {
				set_sign(d, 1);
				retval = (char )retval;
			}
			break;

		case PX_Field_Type_ShortInt:
			copy_from_be(d,s,2);

			if (s[0] & 0x80) {
				fix_sign(d, 2);
			} else if (retval == 0) {
				return VALUE_IS_NULL;
			} else {
				set_sign(d, 2);
				retval = (short)retval;
			}
			break;
		case PX_Field_Type_Incremental:
		case PX_Field_Type_LongInt:
			copy_from_be(d,s,4);

			if (s[0] & 0x80) {
				fix_sign(d, 4);
			} else if (retval == 0) {
				return VALUE_IS_NULL;
			} else {
				set_sign(d, 4);
				retval = (long )retval;
			}
			break;
		default:
			fprintf(stderr,"%s.%d: Can't convert type (%02x)!\n",
				__FILE__, __LINE__,
				type);
			return VALUE_ERROR;

	}
	*ret = retval;
	return VALUE_OK;
}
Ejemplo n.º 2
0
int PXtoDouble(unsigned long long number, double *ret, int type) {
	double retval = 0;
	unsigned char *s = (unsigned char *)&number;
	unsigned char *d = (unsigned char *)&retval;

	switch (type) {
	case PX_Field_Type_Currency:
	case PX_Field_Type_Number:
		copy_from_be(d,s,8);

		if (s[0] & 0x80) {
			/* positive */
			fix_sign(d, 8);
		} else if (retval == 0) {
			return VALUE_IS_NULL;
		} else {
			int i;
			for (i=0; i<8; i++)
				d[i] = ~d[i];
		}
		break;
	default:
		fprintf(stderr,"%s.%d: Can't convert type (%02x)!\n",
			__FILE__, __LINE__,
			type);
		return VALUE_ERROR;
	}
	*ret = retval;
	return VALUE_OK;
}
Ejemplo n.º 3
0
int PXtoTM (unsigned long long number, struct tm *tm, int type ) {
	unsigned long long retval = 0;
	time_t t = 0;
	char *s = (char *)&number;
	char *d = (char *)&retval;
	long jd;
	int y,m,dy;

	struct tm *_tm = tm;

	switch (type) {
		case PX_Field_Type_Date:
			copy_from_be(d,s,4);

			if (s[0] & 0x80) {
				fix_sign(d, 4);
			} else if (retval == 0) {
				return VALUE_IS_NULL;
			} else {
				fprintf(stderr,"%s.%d: DATE can't be nagative\n",
					__FILE__, __LINE__);
				return VALUE_ERROR;
			}

			/* This is Y2K workaround !!!
			** if the date is before 1.1.1970 i add 100 years (365*100 + 24)
			** (seem not to be valid for paradox 7.0)
			*/
#ifdef Y2K_WORKAROUND
			if (retval < 719528) {
				retval += 36524;
			}
#endif
#if 1
			jd = jdatum(1,1,1);
			jd += retval - 1;

			gdate(jd, &y, &m, &dy);

			/* if the date has more than letters
			   we assume that it some inserted correctly
			   (not as an 2 letter short cut.) */

			if (y >= 100)
				_tm->tm_year	= y - 1900;
			else
				_tm->tm_year	= y;

			_tm->tm_mon	= m - 1;
			_tm->tm_mday	= dy;

#else
			t = (retval - 719528 + 365) * 24 * 60 * 60;

			_tm = localtime( &t );
#endif
			break;
		case PX_Field_Type_Time:
			copy_from_be(d,s,4);

			if (s[0] & 0x80) {
				fix_sign(d, 4);
				retval /= 1000; // lost miliseconds !!
				_tm->tm_sec = retval % 60;
				retval /= 60;
				_tm->tm_min = retval % 60;
				_tm->tm_hour = retval/60;
			} else if (retval == 0) {
				return VALUE_IS_NULL;
			} else {
				fprintf(stderr,"%s.%d: TIMESTAMP(%016llx -> %016llx) can't be nagative\n",
					__FILE__, __LINE__,
					number, retval);
				return VALUE_ERROR;
			}
			break;
		case PX_Field_Type_Timestamp:
			copy_from_be(d,s,8);

			if (s[0] & 0x80) {
				fix_sign(d, 8);

			/* the last byte is unused */
				retval >>= 8;

			/* the timestamp seems to have a resolution of 1/500s */
				retval /= 500;

			/* the adjustment that is neccesary to convert paradox
			** timestamp to unix-timestamp [-> time()]
			**
			** FIXME: this value is guessed !!
			** the garantued precission is +/- 1 second
			*/

				retval -= 37603860709183;

				t = retval;

				_tm = gmtime( &t );
			} else if (retval == 0) {
Ejemplo n.º 4
0
Archivo: pow.c Proyecto: tomi500/MPC
/* Put in z the value of x^y, rounded according to 'rnd'.
   Return the inexact flag in [0, 10]. */
int
mpc_pow (mpc_ptr z, mpc_srcptr x, mpc_srcptr y, mpc_rnd_t rnd)
{
  int ret = -2, loop, x_real, x_imag, y_real, z_real = 0, z_imag = 0;
  mpc_t t, u;
  mpfr_prec_t p, pr, pi, maxprec;
  int saved_underflow, saved_overflow;
  
  /* save the underflow or overflow flags from MPFR */
  saved_underflow = mpfr_underflow_p ();
  saved_overflow = mpfr_overflow_p ();

  x_real = mpfr_zero_p (mpc_imagref(x));
  y_real = mpfr_zero_p (mpc_imagref(y));

  if (y_real && mpfr_zero_p (mpc_realref(y))) /* case y zero */
    {
      if (x_real && mpfr_zero_p (mpc_realref(x)))
        {
          /* we define 0^0 to be (1, +0) since the real part is
             coherent with MPFR where 0^0 gives 1, and the sign of the
             imaginary part cannot be determined                       */
          mpc_set_ui_ui (z, 1, 0, MPC_RNDNN);
          return 0;
        }
      else /* x^0 = 1 +/- i*0 even for x=NaN see algorithms.tex for the
              sign of zero */
        {
          mpfr_t n;
          int inex, cx1;
          int sign_zi;
          /* cx1 < 0 if |x| < 1
             cx1 = 0 if |x| = 1
             cx1 > 0 if |x| > 1
          */
          mpfr_init (n);
          inex = mpc_norm (n, x, MPFR_RNDN);
          cx1 = mpfr_cmp_ui (n, 1);
          if (cx1 == 0 && inex != 0)
            cx1 = -inex;

          sign_zi = (cx1 < 0 && mpfr_signbit (mpc_imagref (y)) == 0)
            || (cx1 == 0
                && mpfr_signbit (mpc_imagref (x)) != mpfr_signbit (mpc_realref (y)))
            || (cx1 > 0 && mpfr_signbit (mpc_imagref (y)));

          /* warning: mpc_set_ui_ui does not set Im(z) to -0 if Im(rnd)=RNDD */
          ret = mpc_set_ui_ui (z, 1, 0, rnd);

          if (MPC_RND_IM (rnd) == MPFR_RNDD || sign_zi)
            mpc_conj (z, z, MPC_RNDNN);

          mpfr_clear (n);
          return ret;
        }
    }

  if (!mpc_fin_p (x) || !mpc_fin_p (y))
    {
      /* special values: exp(y*log(x)) */
      mpc_init2 (u, 2);
      mpc_log (u, x, MPC_RNDNN);
      mpc_mul (u, u, y, MPC_RNDNN);
      ret = mpc_exp (z, u, rnd);
      mpc_clear (u);
      goto end;
    }

  if (x_real) /* case x real */
    {
      if (mpfr_zero_p (mpc_realref(x))) /* x is zero */
        {
          /* special values: exp(y*log(x)) */
          mpc_init2 (u, 2);
          mpc_log (u, x, MPC_RNDNN);
          mpc_mul (u, u, y, MPC_RNDNN);
          ret = mpc_exp (z, u, rnd);
          mpc_clear (u);
          goto end;
        }

      /* Special case 1^y = 1 */
      if (mpfr_cmp_ui (mpc_realref(x), 1) == 0)
        {
          int s1, s2;
          s1 = mpfr_signbit (mpc_realref (y));
          s2 = mpfr_signbit (mpc_imagref (x));

          ret = mpc_set_ui (z, +1, rnd);
          /* the sign of the zero imaginary part is known in some cases (see
             algorithm.tex). In such cases we have
             (x +s*0i)^(y+/-0i) = x^y + s*sign(y)*0i
             where s = +/-1.  We extend here this rule to fix the sign of the
             zero part.

             Note that the sign must also be set explicitly when rnd=RNDD
             because mpfr_set_ui(z_i, 0, rnd) always sets z_i to +0.
          */
          if (MPC_RND_IM (rnd) == MPFR_RNDD || s1 != s2)
            mpc_conj (z, z, MPC_RNDNN);
          goto end;
        }

      /* x^y is real when:
         (a) x is real and y is integer
         (b) x is real non-negative and y is real */
      if (y_real && (mpfr_integer_p (mpc_realref(y)) ||
                     mpfr_cmp_ui (mpc_realref(x), 0) >= 0))
        {
          int s1, s2;
          s1 = mpfr_signbit (mpc_realref (y));
          s2 = mpfr_signbit (mpc_imagref (x));

          ret = mpfr_pow (mpc_realref(z), mpc_realref(x), mpc_realref(y), MPC_RND_RE(rnd));
          ret = MPC_INEX(ret, mpfr_set_ui (mpc_imagref(z), 0, MPC_RND_IM(rnd)));

          /* the sign of the zero imaginary part is known in some cases
             (see algorithm.tex). In such cases we have (x +s*0i)^(y+/-0i)
             = x^y + s*sign(y)*0i where s = +/-1.
             We extend here this rule to fix the sign of the zero part.

             Note that the sign must also be set explicitly when rnd=RNDD
             because mpfr_set_ui(z_i, 0, rnd) always sets z_i to +0.
          */
          if (MPC_RND_IM(rnd) == MPFR_RNDD || s1 != s2)
            mpfr_neg (mpc_imagref(z), mpc_imagref(z), MPC_RND_IM(rnd));
          goto end;
        }

      /* (-1)^(n+I*t) is real for n integer and t real */
      if (mpfr_cmp_si (mpc_realref(x), -1) == 0 && mpfr_integer_p (mpc_realref(y)))
        z_real = 1;

      /* for x real, x^y is imaginary when:
         (a) x is negative and y is half-an-integer
         (b) x = -1 and Re(y) is half-an-integer
      */
      if ((mpfr_cmp_ui (mpc_realref(x), 0) < 0) && is_odd (mpc_realref(y), 1)
         && (y_real || mpfr_cmp_si (mpc_realref(x), -1) == 0))
        z_imag = 1;
    }
  else /* x non real */
    /* I^(t*I) and (-I)^(t*I) are real for t real,
       I^(n+t*I) and (-I)^(n+t*I) are real for n even and t real, and
       I^(n+t*I) and (-I)^(n+t*I) are imaginary for n odd and t real
       (s*I)^n is real for n even and imaginary for n odd */
    if ((mpc_cmp_si_si (x, 0, 1) == 0 || mpc_cmp_si_si (x, 0, -1) == 0 ||
         (mpfr_cmp_ui (mpc_realref(x), 0) == 0 && y_real)) &&
        mpfr_integer_p (mpc_realref(y)))
      { /* x is I or -I, and Re(y) is an integer */
        if (is_odd (mpc_realref(y), 0))
          z_imag = 1; /* Re(y) odd: z is imaginary */
        else
          z_real = 1; /* Re(y) even: z is real */
      }
    else /* (t+/-t*I)^(2n) is imaginary for n odd and real for n even */
      if (mpfr_cmpabs (mpc_realref(x), mpc_imagref(x)) == 0 && y_real &&
          mpfr_integer_p (mpc_realref(y)) && is_odd (mpc_realref(y), 0) == 0)
        {
          if (is_odd (mpc_realref(y), -1)) /* y/2 is odd */
            z_imag = 1;
          else
            z_real = 1;
        }

  pr = mpfr_get_prec (mpc_realref(z));
  pi = mpfr_get_prec (mpc_imagref(z));
  p = (pr > pi) ? pr : pi;
  p += 12; /* experimentally, seems to give less than 10% of failures in
              Ziv's strategy; probably wrong now since q is not computed */
  if (p < 64)
    p = 64;
  mpc_init2 (u, p);
  mpc_init2 (t, p);
  pr += MPC_RND_RE(rnd) == MPFR_RNDN;
  pi += MPC_RND_IM(rnd) == MPFR_RNDN;
  maxprec = MPC_MAX_PREC (z);
  x_imag = mpfr_zero_p (mpc_realref(x));
  for (loop = 0;; loop++)
    {
      int ret_exp;
      mpfr_exp_t dr, di;
      mpfr_prec_t q;

      mpc_log (t, x, MPC_RNDNN);
      mpc_mul (t, t, y, MPC_RNDNN);

      /* Compute q such that |Re (y log x)|, |Im (y log x)| < 2^q.
         We recompute it at each loop since we might get different
         bounds if the precision is not enough. */
      q = mpfr_get_exp (mpc_realref(t)) > 0 ? mpfr_get_exp (mpc_realref(t)) : 0;
      if (mpfr_get_exp (mpc_imagref(t)) > (mpfr_exp_t) q)
        q = mpfr_get_exp (mpc_imagref(t));

      mpfr_clear_overflow ();
      mpfr_clear_underflow ();
      ret_exp = mpc_exp (u, t, MPC_RNDNN);
      if (mpfr_underflow_p () || mpfr_overflow_p ()) {
         /* under- and overflow flags are set by mpc_exp */
         mpc_set (z, u, MPC_RNDNN);
         ret = ret_exp;
         goto exact;
      }

      /* Since the error bound is global, we have to take into account the
         exponent difference between the real and imaginary parts. We assume
         either the real or the imaginary part of u is not zero.
      */
      dr = mpfr_zero_p (mpc_realref(u)) ? mpfr_get_exp (mpc_imagref(u))
        : mpfr_get_exp (mpc_realref(u));
      di = mpfr_zero_p (mpc_imagref(u)) ? dr : mpfr_get_exp (mpc_imagref(u));
      if (dr > di)
        {
          di = dr - di;
          dr = 0;
        }
      else
        {
          dr = di - dr;
          di = 0;
        }
      /* the term -3 takes into account the factor 4 in the complex error
         (see algorithms.tex) plus one due to the exponent difference: if
         z = a + I*b, where the relative error on z is at most 2^(-p), and
         EXP(a) = EXP(b) + k, the relative error on b is at most 2^(k-p) */
      if ((z_imag || (p > q + 3 + dr && mpfr_can_round (mpc_realref(u), p - q - 3 - dr, MPFR_RNDN, MPFR_RNDZ, pr))) &&
          (z_real || (p > q + 3 + di && mpfr_can_round (mpc_imagref(u), p - q - 3 - di, MPFR_RNDN, MPFR_RNDZ, pi))))
        break;

      /* if Re(u) is not known to be zero, assume it is a normal number, i.e.,
         neither zero, Inf or NaN, otherwise we might enter an infinite loop */
      MPC_ASSERT (z_imag || mpfr_number_p (mpc_realref(u)));
      /* idem for Im(u) */
      MPC_ASSERT (z_real || mpfr_number_p (mpc_imagref(u)));

      if (ret == -2) /* we did not yet call mpc_pow_exact, or it aborted
                        because intermediate computations had > maxprec bits */
        {
          /* check exact cases (see algorithms.tex) */
          if (y_real)
            {
              maxprec *= 2;
              ret = mpc_pow_exact (z, x, mpc_realref(y), rnd, maxprec);
              if (ret != -1 && ret != -2)
                goto exact;
            }
          p += dr + di + 64;
        }
      else
        p += p / 2;
      mpc_set_prec (t, p);
      mpc_set_prec (u, p);
    }

  if (z_real)
    {
      /* When the result is real (see algorithm.tex for details),
         Im(x^y) =
         + sign(imag(y))*0i,               if |x| > 1
         + sign(imag(x))*sign(real(y))*0i, if |x| = 1
         - sign(imag(y))*0i,               if |x| < 1
      */
      mpfr_t n;
      int inex, cx1;
      int sign_zi, sign_rex, sign_imx;
      /* cx1 < 0 if |x| < 1
         cx1 = 0 if |x| = 1
         cx1 > 0 if |x| > 1
      */

      sign_rex = mpfr_signbit (mpc_realref (x));
      sign_imx = mpfr_signbit (mpc_imagref (x));
      mpfr_init (n);
      inex = mpc_norm (n, x, MPFR_RNDN);
      cx1 = mpfr_cmp_ui (n, 1);
      if (cx1 == 0 && inex != 0)
        cx1 = -inex;

      sign_zi = (cx1 < 0 && mpfr_signbit (mpc_imagref (y)) == 0)
        || (cx1 == 0 && sign_imx != mpfr_signbit (mpc_realref (y)))
        || (cx1 > 0 && mpfr_signbit (mpc_imagref (y)));

      /* copy RE(y) to n since if z==y we will destroy Re(y) below */
      mpfr_set_prec (n, mpfr_get_prec (mpc_realref (y)));
      mpfr_set (n, mpc_realref (y), MPFR_RNDN);
      ret = mpfr_set (mpc_realref(z), mpc_realref(u), MPC_RND_RE(rnd));
      if (y_real && (x_real || x_imag))
        {
          /* FIXME: with y_real we assume Im(y) is really 0, which is the case
             for example when y comes from pow_fr, but in case Im(y) is +0 or
             -0, we might get different results */
          mpfr_set_ui (mpc_imagref (z), 0, MPC_RND_IM (rnd));
          fix_sign (z, sign_rex, sign_imx, n);
          ret = MPC_INEX(ret, 0); /* imaginary part is exact */
        }
      else
        {
          ret = MPC_INEX (ret, mpfr_set_ui (mpc_imagref (z), 0, MPC_RND_IM (rnd)));
          /* warning: mpfr_set_ui does not set Im(z) to -0 if Im(rnd) = RNDD */
          if (MPC_RND_IM (rnd) == MPFR_RNDD || sign_zi)
            mpc_conj (z, z, MPC_RNDNN);
        }

      mpfr_clear (n);
    }
  else if (z_imag)
    {
      ret = mpfr_set (mpc_imagref(z), mpc_imagref(u), MPC_RND_IM(rnd));
      /* if z is imaginary and y real, then x cannot be real */
      if (y_real && x_imag)
        {
          int sign_rex = mpfr_signbit (mpc_realref (x));

          /* If z overlaps with y we set Re(z) before checking Re(y) below,
             but in that case y=0, which was dealt with above. */
          mpfr_set_ui (mpc_realref (z), 0, MPC_RND_RE (rnd));
          /* Note: fix_sign only does something when y is an integer,
             then necessarily y = 1 or 3 (mod 4), and in that case the
             sign of Im(x) is irrelevant. */
          fix_sign (z, sign_rex, 0, mpc_realref (y));
          ret = MPC_INEX(0, ret);
        }
      else
        ret = MPC_INEX(mpfr_set_ui (mpc_realref(z), 0, MPC_RND_RE(rnd)), ret);
    }
  else
    ret = mpc_set (z, u, rnd);
 exact:
  mpc_clear (t);
  mpc_clear (u);

  /* restore underflow and overflow flags from MPFR */
  if (saved_underflow)
    mpfr_set_underflow ();
  if (saved_overflow)
    mpfr_set_overflow ();

 end:
  return ret;
}
Ejemplo n.º 5
0
Archivo: pow.c Proyecto: tomi500/MPC
/* 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).

   Warning: z and x might be the same variable, same for Re(z) or Im(z) and y.

   In case -1 or -2 is returned, z is not modified.
*/
static int
mpc_pow_exact (mpc_ptr z, mpc_srcptr x, mpfr_srcptr y, mpc_rnd_t rnd,
               mpfr_prec_t maxprec)
{
  mpfr_exp_t ec, ed, ey;
  mpz_t my, a, b, c, d, u;
  unsigned long int t;
  int ret = -2;
  int sign_rex = mpfr_signbit (mpc_realref(x));
  int sign_imx = mpfr_signbit (mpc_imagref(x));
  int x_imag = mpfr_zero_p (mpc_realref(x));
  int z_is_y = 0;
  mpfr_t copy_of_y;

  if (mpc_realref (z) == y || mpc_imagref (z) == y)
    {
      z_is_y = 1;
      mpfr_init2 (copy_of_y, mpfr_get_prec (y));
      mpfr_set (copy_of_y, y, MPFR_RNDN);
    }

  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 += (mpfr_exp_t) t;
  mpz_tdiv_q_2exp (my, my, t);
  /* y = my*2^ey with my odd */

  if (x_imag)
    {
      mpz_set_ui (c, 0);
      ec = 0;
    }
  else
    ec = mpfr_get_z_exp (c, mpc_realref(x));
  if (mpfr_zero_p (mpc_imagref(x)))
    {
      mpz_set_ui (d, 0);
      ed = ec;
    }
  else
    {
      ed = mpfr_get_z_exp (d, mpc_imagref(x));
      if (x_imag)
        ec = ed;
    }
  /* x = c*2^ec + I * d*2^ed */
  /* equalize the exponents of x */
  if (ec < ed)
    {
      mpz_mul_2exp (d, d, (unsigned long int) (ed - ec));
      if ((mpfr_prec_t) mpz_sizeinbase (d, 2) > maxprec)
        goto end;
    }
  else if (ed < ec)
    {
      mpz_mul_2exp (c, c, (unsigned long int) (ec - ed));
      if ((mpfr_prec_t) 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 += (mpfr_exp_t) t;
    }
  else if (mpz_cmp_ui (d, 0) == 0)
    {
      t = mpz_scan1 (c, 0);
      mpz_tdiv_q_2exp (c, c, t);
      ec += (mpfr_exp_t) 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 += (mpfr_exp_t) 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 - (mpfr_exp_t) 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 int 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 += (mpfr_exp_t) w;
        }
      else if (mpz_cmp_ui (b, 0) == 0)
        {
          w = mpz_scan1 (a, 0);
          mpz_tdiv_q_2exp (a, a, w);
          ed += (mpfr_exp_t) 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 += (mpfr_exp_t) w;
        }
      if (   (mpfr_prec_t) mpz_sizeinbase (a, 2) > maxprec
          || (mpfr_prec_t) 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 += (mpfr_exp_t) sa;

      if (   (mpfr_prec_t) mpz_sizeinbase (a, 2) > maxprec
          || (mpfr_prec_t) mpz_sizeinbase (b, 2) > maxprec)
        goto end;
    }

  ret = mpfr_set_z (mpc_realref(z), a, MPC_RND_RE(rnd));
  ret = MPC_INEX(ret, mpfr_set_z (mpc_imagref(z), b, MPC_RND_IM(rnd)));
  mpfr_mul_2si (mpc_realref(z), mpc_realref(z), ed, MPC_RND_RE(rnd));
  mpfr_mul_2si (mpc_imagref(z), mpc_imagref(z), ed, MPC_RND_IM(rnd));

 end:
  mpz_clear (my);
  mpz_clear (a);
  mpz_clear (b);
  mpz_clear (c);
  mpz_clear (d);
  mpz_clear (u);

  if (ret >= 0 && x_imag)
    fix_sign (z, sign_rex, sign_imx, (z_is_y) ? copy_of_y : y);

  if (z_is_y)
    mpfr_clear (copy_of_y);

  return ret;
}