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Annotation of OpenXM_contrib/gmp/mpfr/tan.c, Revision 1.1.1.1

1.1       ohara       1: /* mpfr_tan -- tangent of a floating-point number
                      2:
                      3: Copyright 2001, 2002 Free Software Foundation, Inc.
                      4:
                      5: This file is part of the MPFR Library.
                      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 "gmp.h"
                     23: #include "gmp-impl.h"
                     24: #include "mpfr.h"
                     25: #include "mpfr-impl.h"
                     26:
                     27: /* computes tan(x) = sign(x)*sqrt(1/cos(x)^2-1) */
                     28: int
                     29: mpfr_tan (mpfr_ptr y, mpfr_srcptr x, mp_rnd_t rnd_mode)
                     30: {
                     31:   int precy, m, ok, inexact;
                     32:   mpfr_t s, c;
                     33:
                     34:   if (MPFR_IS_NAN(x) || MPFR_IS_INF(x))
                     35:     {
                     36:       MPFR_SET_NAN(y);
                     37:       MPFR_RET_NAN;
                     38:     }
                     39:
                     40:   if (MPFR_IS_ZERO(x))
                     41:     {
                     42:       MPFR_CLEAR_FLAGS(y);
                     43:       MPFR_SET_ZERO(y);
                     44:       MPFR_SET_SAME_SIGN(y, x);
                     45:       MPFR_RET(0);
                     46:     }
                     47:
                     48:   precy = MPFR_PREC(y);
                     49:   m = precy + _mpfr_ceil_log2 ((double) precy) + ABS(MPFR_EXP(x)) + 13;
                     50:
                     51:   mpfr_init2 (s, m);
                     52:   mpfr_init2 (c, m);
                     53:
                     54:   do
                     55:     {
                     56:       mpfr_sin_cos (s, c, x, GMP_RNDN); /* err <= 1/2 ulp on s and c */
                     57:       mpfr_div (c, s, c, GMP_RNDN);     /* err <= 2 ulps */
                     58:       ok = mpfr_can_round (c, m - 1, GMP_RNDN, rnd_mode, precy);
                     59:
                     60:       if (ok == 0)
                     61:        {
                     62:          m += BITS_PER_MP_LIMB;
                     63:          mpfr_set_prec (s, m);
                     64:          mpfr_set_prec (c, m);
                     65:        }
                     66:     }
                     67:   while (!ok);
                     68:
                     69:   inexact = mpfr_set (y, c, rnd_mode);
                     70:
                     71:   mpfr_clear (s);
                     72:   mpfr_clear (c);
                     73:
                     74:   return inexact;
                     75: }