source/libs/mpfr/mpfr-3.1.3/src/sinh.c

   1 /* mpfr_sinh -- hyperbolic sine
   2
   3 Copyright 2001-2015 Free Software Foundation, Inc.
   4 Contributed by the AriC and Caramel projects, INRIA.
   5
   6 This file is part of the GNU MPFR Library.
   7
   8 The GNU MPFR Library is free software; you can redistribute it and/or modify
   9 it under the terms of the GNU Lesser General Public License as published by
  10 the Free Software Foundation; either version 3 of the License, or (at your
  11 option) any later version.
  12
  13 The GNU MPFR Library is distributed in the hope that it will be useful, but
  14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  15 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  16 License for more details.
  17
  18 You should have received a copy of the GNU Lesser General Public License
  19 along with the GNU MPFR Library; see the file COPYING.LESSER.  If not, see
  20 http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
  21 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
  22
  23 #define MPFR_NEED_LONGLONG_H
  24 #include "mpfr-impl.h"
  25
  26  /* The computation of sinh is done by
  27     sinh(x) = 1/2 [e^(x)-e^(-x)]          */
  28
  29 int
  30 mpfr_sinh (mpfr_ptr y, mpfr_srcptr xt, mpfr_rnd_t rnd_mode)
  31 {
  32   mpfr_t x;
  33   int inexact;
  34
  35   MPFR_LOG_FUNC
  36     (("x[%Pu]=%.*Rg rnd=%d", mpfr_get_prec (xt), mpfr_log_prec, xt, rnd_mode),
  37      ("y[%Pu]=%.*Rg inexact=%d",
  38       mpfr_get_prec (y), mpfr_log_prec, y, inexact));
  39
  40   if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (xt)))
  41     {
  42       if (MPFR_IS_NAN (xt))
  43         {
  44           MPFR_SET_NAN (y);
  45           MPFR_RET_NAN;
  46         }
  47       else if (MPFR_IS_INF (xt))
  48         {
  49           MPFR_SET_INF (y);
  50           MPFR_SET_SAME_SIGN (y, xt);
  51           MPFR_RET (0);
  52         }
  53       else /* xt is zero */
  54         {
  55           MPFR_ASSERTD (MPFR_IS_ZERO (xt));
  56           MPFR_SET_ZERO (y);   /* sinh(0) = 0 */
  57           MPFR_SET_SAME_SIGN (y, xt);
  58           MPFR_RET (0);
  59         }
  60     }
  61
  62   /* sinh(x) = x + x^3/6 + ... so the error is < 2^(3*EXP(x)-2) */
  63   MPFR_FAST_COMPUTE_IF_SMALL_INPUT (y, xt, -2 * MPFR_GET_EXP(xt), 2, 1,
  64                                     rnd_mode, {});
  65
  66   MPFR_TMP_INIT_ABS (x, xt);
  67
  68   {
  69     mpfr_t t, ti;
  70     mpfr_exp_t d;
  71     mpfr_prec_t Nt;    /* Precision of the intermediary variable */
  72     long int err;    /* Precision of error */
  73     MPFR_ZIV_DECL (loop);
  74     MPFR_SAVE_EXPO_DECL (expo);
  75     MPFR_GROUP_DECL (group);
  76
  77     MPFR_SAVE_EXPO_MARK (expo);
  78
  79     /* compute the precision of intermediary variable */
  80     Nt = MAX (MPFR_PREC (x), MPFR_PREC (y));
  81     /* the optimal number of bits : see algorithms.ps */
  82     Nt = Nt + MPFR_INT_CEIL_LOG2 (Nt) + 4;
  83     /* If x is near 0, exp(x) - 1/exp(x) = 2*x+x^3/3+O(x^5) */
  84     if (MPFR_GET_EXP (x) < 0)
  85       Nt -= 2*MPFR_GET_EXP (x);
  86
  87     /* initialise of intermediary variables */
  88     MPFR_GROUP_INIT_2 (group, Nt, t, ti);
  89
  90     /* First computation of sinh */
  91     MPFR_ZIV_INIT (loop, Nt);
  92     for (;;)
  93       {
  94         MPFR_BLOCK_DECL (flags);
  95
  96         /* compute sinh */
  97         MPFR_BLOCK (flags, mpfr_exp (t, x, MPFR_RNDD));
  98         if (MPFR_OVERFLOW (flags))
  99           /* exp(x) does overflow */
 100           {
 101             /* sinh(x) = 2 * sinh(x/2) * cosh(x/2) */
 102             mpfr_div_2ui (ti, x, 1, MPFR_RNDD); /* exact */
 103
 104             /* t <- cosh(x/2): error(t) <= 1 ulp(t) */
 105             MPFR_BLOCK (flags, mpfr_cosh (t, ti, MPFR_RNDD));
 106             if (MPFR_OVERFLOW (flags))
 107               /* when x>1 we have |sinh(x)| >= cosh(x/2), so sinh(x)
 108                  overflows too */
 109               {
 110                 inexact = mpfr_overflow (y, rnd_mode, MPFR_SIGN (xt));
 111                 MPFR_SAVE_EXPO_UPDATE_FLAGS (expo, MPFR_FLAGS_OVERFLOW);
 112                 break;
 113               }
 114
 115             /* ti <- sinh(x/2): , error(ti) <= 1 ulp(ti)
 116                cannot overflow because 0 < sinh(x) < cosh(x) when x > 0 */
 117             mpfr_sinh (ti, ti, MPFR_RNDD);
 118
 119             /* multiplication below, error(t) <= 5 ulp(t) */
 120             MPFR_BLOCK (flags, mpfr_mul (t, t, ti, MPFR_RNDD));
 121             if (MPFR_OVERFLOW (flags))
 122               {
 123                 inexact = mpfr_overflow (y, rnd_mode, MPFR_SIGN (xt));
 124                 MPFR_SAVE_EXPO_UPDATE_FLAGS (expo, MPFR_FLAGS_OVERFLOW);
 125                 break;
 126               }
 127
 128             /* doubling below, exact */
 129             MPFR_BLOCK (flags, mpfr_mul_2ui (t, t, 1, MPFR_RNDN));
 130             if (MPFR_OVERFLOW (flags))
 131               {
 132                 inexact = mpfr_overflow (y, rnd_mode, MPFR_SIGN (xt));
 133                 MPFR_SAVE_EXPO_UPDATE_FLAGS (expo, MPFR_FLAGS_OVERFLOW);
 134                 break;
 135               }
 136
 137             /* we have lost at most 3 bits of precision */
 138             err = Nt - 3;
 139             if (MPFR_LIKELY (MPFR_CAN_ROUND (t, err, MPFR_PREC (y),
 140                                              rnd_mode)))
 141               {
 142                 inexact = mpfr_set4 (y, t, rnd_mode, MPFR_SIGN (xt));
 143                 break;
 144               }
 145             err = Nt; /* double the precision */
 146           }
 147         else
 148           {
 149             d = MPFR_GET_EXP (t);
 150             mpfr_ui_div (ti, 1, t, MPFR_RNDU); /* 1/exp(x) */
 151             mpfr_sub (t, t, ti, MPFR_RNDN);    /* exp(x) - 1/exp(x) */
 152             mpfr_div_2ui (t, t, 1, MPFR_RNDN);  /* 1/2(exp(x) - 1/exp(x)) */
 153
 154             /* it may be that t is zero (in fact, it can only occur when te=1,
 155                and thus ti=1 too) */
 156             if (MPFR_IS_ZERO (t))
 157               err = Nt; /* double the precision */
 158             else
 159               {
 160                 /* calculation of the error */
 161                 d = d - MPFR_GET_EXP (t) + 2;
 162                 /* error estimate: err = Nt-(__gmpfr_ceil_log2(1+pow(2,d)));*/
 163                 err = Nt - (MAX (d, 0) + 1);
 164                 if (MPFR_LIKELY (MPFR_CAN_ROUND (t, err, MPFR_PREC (y),
 165                                                  rnd_mode)))
 166                   {
 167                     inexact = mpfr_set4 (y, t, rnd_mode, MPFR_SIGN (xt));
 168                     break;
 169                   }
 170               }
 171           }
 172
 173         /* actualisation of the precision */
 174         Nt += err;
 175         MPFR_ZIV_NEXT (loop, Nt);
 176         MPFR_GROUP_REPREC_2 (group, Nt, t, ti);
 177       }
 178     MPFR_ZIV_FREE (loop);
 179     MPFR_GROUP_CLEAR (group);
 180     MPFR_SAVE_EXPO_FREE (expo);
 181   }
 182
 183   return mpfr_check_range (y, inexact, rnd_mode);
 184 }