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Annotation of OpenXM_contrib/gmp/mpfr/acos.c, Revision 1.1

1.1     ! ohara       1: /* mpfr_acos -- arc-cosinus of a floating-point number
        !             2:
        !             3: Copyright 2001 Free Software Foundation.
        !             4:
        !             5: This file is part of the MPFR Library, and was contributed by Mathieu Dutour.
        !             6:
        !             7: The MPFR Library is free software; you can redistribute it and/or modify
        !             8: it under the terms of the GNU Lesser General Public License as published by
        !             9: the Free Software Foundation; either version 2.1 of the License, or (at your
        !            10: option) any later version.
        !            11:
        !            12: The MPFR Library is distributed in the hope that it will be useful, but
        !            13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
        !            14: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
        !            15: License for more details.
        !            16:
        !            17: You should have received a copy of the GNU Lesser General Public License
        !            18: along with the MPFR Library; see the file COPYING.LIB.  If not, write to
        !            19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
        !            20: MA 02111-1307, USA. */
        !            21:
        !            22: #include <stdio.h>
        !            23: #include <stdlib.h>
        !            24: #include "gmp.h"
        !            25: #include "gmp-impl.h"
        !            26: #include "mpfr.h"
        !            27: #include "mpfr-impl.h"
        !            28:
        !            29: int
        !            30: mpfr_acos (mpfr_ptr acos, mpfr_srcptr x, mp_rnd_t rnd_mode)
        !            31: {
        !            32:   mpfr_t xp;
        !            33:   mpfr_t arcc;
        !            34:
        !            35:   int signe, suplement;
        !            36:
        !            37:   mpfr_t tmp;
        !            38:   int Prec;
        !            39:   int prec_acos;
        !            40:   int good = 0;
        !            41:   int realprec;
        !            42:   int compared;
        !            43:   int inexact = 0;
        !            44:
        !            45:   /* Trivial cases */
        !            46:   if (MPFR_IS_NAN(x) || MPFR_IS_INF(x))
        !            47:     {
        !            48:       MPFR_SET_NAN(acos);
        !            49:       MPFR_RET_NAN;
        !            50:     }
        !            51:
        !            52:   /* Set x_p=|x| */
        !            53:   signe = MPFR_SIGN(x);
        !            54:   mpfr_init2 (xp, MPFR_PREC(x));
        !            55:   mpfr_abs (xp, x, rnd_mode);
        !            56:
        !            57:   compared = mpfr_cmp_ui (xp, 1);
        !            58:
        !            59:   if (compared > 0) /* acos(x) = NaN for x > 1 */
        !            60:     {
        !            61:       mpfr_clear (xp);
        !            62:       MPFR_SET_NAN(acos);
        !            63:       MPFR_RET_NAN;
        !            64:     }
        !            65:
        !            66:   if (compared == 0)
        !            67:     {
        !            68:       mpfr_clear (xp);
        !            69:       if (signe > 0) /* acos(+1) = 0 */
        !            70:        return mpfr_set_ui (acos, 0, rnd_mode);
        !            71:       else /* acos(-1) = Pi */
        !            72:         {
        !            73:           mpfr_const_pi (acos, rnd_mode);
        !            74:           return 1; /* inexact */
        !            75:         }
        !            76:     }
        !            77:
        !            78:   if (MPFR_IS_ZERO(x)) /* acos(0)=Pi/2 */
        !            79:     {
        !            80:       mpfr_clear (xp);
        !            81:       mpfr_const_pi (acos, rnd_mode);
        !            82:       MPFR_EXP(acos)--;
        !            83:       return 1; /* inexact */
        !            84:     }
        !            85:
        !            86:   prec_acos = MPFR_PREC(acos);
        !            87:   mpfr_ui_sub (xp, 1, xp, GMP_RNDD);
        !            88:
        !            89:   if (signe > 0)
        !            90:       suplement = 2 - 2 * MPFR_EXP(xp);
        !            91:   else
        !            92:       suplement = 2 - MPFR_EXP(xp);
        !            93:
        !            94:   realprec = prec_acos + 10;
        !            95:
        !            96:   while (!good)
        !            97:     {
        !            98:       Prec = realprec+suplement;
        !            99:
        !           100:       /* Initialisation    */
        !           101:       mpfr_init2 (tmp, Prec);
        !           102:       mpfr_init2 (arcc, Prec);
        !           103:
        !           104:       mpfr_mul (tmp, x, x, GMP_RNDN);
        !           105:       mpfr_ui_sub (tmp, 1, tmp, GMP_RNDN);
        !           106:       mpfr_sqrt (tmp, tmp, GMP_RNDN);
        !           107:       mpfr_div (tmp, x, tmp, GMP_RNDN);
        !           108:       mpfr_atan (arcc, tmp, GMP_RNDN);
        !           109:       mpfr_const_pi (tmp, GMP_RNDN);
        !           110:       mpfr_div_2ui (tmp, tmp, 1, GMP_RNDN);
        !           111:       mpfr_sub (arcc, tmp, arcc, GMP_RNDN);
        !           112:
        !           113:       if (mpfr_can_round (arcc, realprec, GMP_RNDN, rnd_mode, MPFR_PREC(acos)))
        !           114:         {
        !           115:           inexact = mpfr_set (acos, arcc, rnd_mode);
        !           116:           good = 1;
        !           117:         }
        !           118:       else
        !           119:         realprec += _mpfr_ceil_log2 ((double) realprec);
        !           120:
        !           121:     mpfr_clear (tmp);
        !           122:     mpfr_clear (arcc);
        !           123:   }
        !           124:
        !           125:   mpfr_clear (xp);
        !           126:   return inexact;
        !           127: }