/* mpc_acos -- arccosine of a complex number. Copyright (C) 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 /* for MPC_ASSERT */ #include "mpc-impl.h" int mpc_acos (mpc_ptr rop, mpc_srcptr op, mpc_rnd_t rnd) { int inex_re, inex_im, inex; mpfr_prec_t p_re, p_im, p; mpc_t z1; mpfr_t pi_over_2; mpfr_exp_t e1, e2; mpfr_rnd_t rnd_im; mpc_rnd_t rnd1; inex_re = 0; inex_im = 0; /* special values */ if (mpfr_nan_p (mpc_realref (op)) || mpfr_nan_p (mpc_imagref (op))) { if (mpfr_inf_p (mpc_realref (op)) || mpfr_inf_p (mpc_imagref (op))) { mpfr_set_inf (mpc_imagref (rop), mpfr_signbit (mpc_imagref (op)) ? +1 : -1); mpfr_set_nan (mpc_realref (rop)); } else if (mpfr_zero_p (mpc_realref (op))) { inex_re = set_pi_over_2 (mpc_realref (rop), +1, MPC_RND_RE (rnd)); mpfr_set_nan (mpc_imagref (rop)); } else { mpfr_set_nan (mpc_realref (rop)); mpfr_set_nan (mpc_imagref (rop)); } return MPC_INEX (inex_re, 0); } if (mpfr_inf_p (mpc_realref (op)) || mpfr_inf_p (mpc_imagref (op))) { if (mpfr_inf_p (mpc_realref (op))) { if (mpfr_inf_p (mpc_imagref (op))) { if (mpfr_sgn (mpc_realref (op)) > 0) { inex_re = set_pi_over_2 (mpc_realref (rop), +1, MPC_RND_RE (rnd)); mpfr_div_2ui (mpc_realref (rop), mpc_realref (rop), 1, GMP_RNDN); } else { /* the real part of the result is 3*pi/4 a = o(pi) error(a) < 1 ulp(a) b = o(3*a) error(b) < 2 ulp(b) c = b/4 exact thus 1 bit is lost */ mpfr_t x; mpfr_prec_t prec; int ok; mpfr_init (x); prec = mpfr_get_prec (mpc_realref (rop)); p = prec; do { p += mpc_ceil_log2 (p); mpfr_set_prec (x, p); mpfr_const_pi (x, GMP_RNDD); mpfr_mul_ui (x, x, 3, GMP_RNDD); ok = mpfr_can_round (x, p - 1, GMP_RNDD, MPC_RND_RE (rnd), prec+(MPC_RND_RE (rnd) == GMP_RNDN)); } while (ok == 0); inex_re = mpfr_div_2ui (mpc_realref (rop), x, 2, MPC_RND_RE (rnd)); mpfr_clear (x); } } else { if (mpfr_sgn (mpc_realref (op)) > 0) mpfr_set_ui (mpc_realref (rop), 0, GMP_RNDN); else inex_re = mpfr_const_pi (mpc_realref (rop), MPC_RND_RE (rnd)); } } else inex_re = set_pi_over_2 (mpc_realref (rop), +1, MPC_RND_RE (rnd)); mpfr_set_inf (mpc_imagref (rop), mpfr_signbit (mpc_imagref (op)) ? +1 : -1); return MPC_INEX (inex_re, 0); } /* pure real argument */ if (mpfr_zero_p (mpc_imagref (op))) { int s_im; s_im = mpfr_signbit (mpc_imagref (op)); if (mpfr_cmp_ui (mpc_realref (op), 1) > 0) { if (s_im) inex_im = mpfr_acosh (mpc_imagref (rop), mpc_realref (op), MPC_RND_IM (rnd)); else inex_im = -mpfr_acosh (mpc_imagref (rop), mpc_realref (op), INV_RND (MPC_RND_IM (rnd))); mpfr_set_ui (mpc_realref (rop), 0, GMP_RNDN); } else if (mpfr_cmp_si (mpc_realref (op), -1) < 0) { mpfr_t minus_op_re; minus_op_re[0] = mpc_realref (op)[0]; MPFR_CHANGE_SIGN (minus_op_re); if (s_im) inex_im = mpfr_acosh (mpc_imagref (rop), minus_op_re, MPC_RND_IM (rnd)); else inex_im = -mpfr_acosh (mpc_imagref (rop), minus_op_re, INV_RND (MPC_RND_IM (rnd))); inex_re = mpfr_const_pi (mpc_realref (rop), MPC_RND_RE (rnd)); } else { inex_re = mpfr_acos (mpc_realref (rop), mpc_realref (op), MPC_RND_RE (rnd)); mpfr_set_ui (mpc_imagref (rop), 0, MPC_RND_IM (rnd)); } if (!s_im) mpc_conj (rop, rop, MPC_RNDNN); return MPC_INEX (inex_re, inex_im); } /* pure imaginary argument */ if (mpfr_zero_p (mpc_realref (op))) { inex_re = set_pi_over_2 (mpc_realref (rop), +1, MPC_RND_RE (rnd)); inex_im = -mpfr_asinh (mpc_imagref (rop), mpc_imagref (op), INV_RND (MPC_RND_IM (rnd))); mpc_conj (rop,rop, MPC_RNDNN); return MPC_INEX (inex_re, inex_im); } /* regular complex argument: acos(z) = Pi/2 - asin(z) */ p_re = mpfr_get_prec (mpc_realref(rop)); p_im = mpfr_get_prec (mpc_imagref(rop)); p = p_re; mpc_init3 (z1, p, p_im); /* we round directly the imaginary part to p_im, with rounding mode opposite to rnd_im */ rnd_im = MPC_RND_IM(rnd); /* the imaginary part of asin(z) has the same sign as Im(z), thus if Im(z) > 0 and rnd_im = RNDZ, we want to round the Im(asin(z)) to -Inf so that -Im(asin(z)) is rounded to zero */ if (rnd_im == GMP_RNDZ) rnd_im = mpfr_sgn (mpc_imagref(op)) > 0 ? GMP_RNDD : GMP_RNDU; else rnd_im = rnd_im == GMP_RNDU ? GMP_RNDD : rnd_im == GMP_RNDD ? GMP_RNDU : rnd_im; /* both RNDZ and RNDA map to themselves for -asin(z) */ rnd1 = MPC_RND (GMP_RNDN, rnd_im); mpfr_init2 (pi_over_2, p); for (;;) { p += mpc_ceil_log2 (p) + 3; mpfr_set_prec (mpc_realref(z1), p); mpfr_set_prec (pi_over_2, p); set_pi_over_2 (pi_over_2, +1, GMP_RNDN); e1 = 1; /* Exp(pi_over_2) */ inex = mpc_asin (z1, op, rnd1); /* asin(z) */ MPC_ASSERT (mpfr_sgn (mpc_imagref(z1)) * mpfr_sgn (mpc_imagref(op)) > 0); inex_im = MPC_INEX_IM(inex); /* inex_im is in {-1, 0, 1} */ e2 = mpfr_get_exp (mpc_realref(z1)); mpfr_sub (mpc_realref(z1), pi_over_2, mpc_realref(z1), GMP_RNDN); if (!mpfr_zero_p (mpc_realref(z1))) { /* the error on x=Re(z1) is bounded by 1/2 ulp(x) + 2^(e1-p-1) + 2^(e2-p-1) */ e1 = e1 >= e2 ? e1 + 1 : e2 + 1; /* the error on x is bounded by 1/2 ulp(x) + 2^(e1-p-1) */ e1 -= mpfr_get_exp (mpc_realref(z1)); /* the error on x is bounded by 1/2 ulp(x) [1 + 2^e1] */ e1 = e1 <= 0 ? 0 : e1; /* the error on x is bounded by 2^e1 * ulp(x) */ mpfr_neg (mpc_imagref(z1), mpc_imagref(z1), GMP_RNDN); /* exact */ inex_im = -inex_im; if (mpfr_can_round (mpc_realref(z1), p - e1, GMP_RNDN, GMP_RNDZ, p_re + (MPC_RND_RE(rnd) == GMP_RNDN))) break; } } inex = mpc_set (rop, z1, rnd); inex_re = MPC_INEX_RE(inex); mpc_clear (z1); mpfr_clear (pi_over_2); return MPC_INEX(inex_re, inex_im); }