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Annotation of OpenXM_contrib/gmp/mpfr/expm1.c, Revision 1.1

1.1     ! ohara       1: /* mpfr_expm1 -- Compute exp(x)-1
        !             2:
        !             3: Copyright 2001, 2002 Free Software Foundation.
        !             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:  /* The computation of expm1 is done by
        !            28:
        !            29:     expm1(x)=exp(x)-1
        !            30:  */
        !            31:
        !            32: int
        !            33: mpfr_expm1 (mpfr_ptr y, mpfr_srcptr x , mp_rnd_t rnd_mode)
        !            34: {
        !            35:   int inexact = 0;
        !            36:
        !            37:   if (MPFR_IS_NAN(x))
        !            38:     {
        !            39:       MPFR_SET_NAN(y);
        !            40:       MPFR_RET_NAN;
        !            41:     }
        !            42:
        !            43:   MPFR_CLEAR_NAN(y);
        !            44:
        !            45:   /* check for inf or -inf (expm1(-inf)=-1) */
        !            46:   if (MPFR_IS_INF(x))
        !            47:     {
        !            48:       if (MPFR_SIGN(x) > 0)
        !            49:         {
        !            50:           MPFR_SET_INF(y);
        !            51:           MPFR_SET_POS(y);
        !            52:           return 0;
        !            53:         }
        !            54:       else
        !            55:         return mpfr_set_si(y, -1, rnd_mode);
        !            56:     }
        !            57:
        !            58:   MPFR_CLEAR_INF(y);
        !            59:
        !            60:   if(MPFR_IS_ZERO(x))
        !            61:     {
        !            62:       MPFR_SET_ZERO(y);   /* expm1(+/- 0) = +/- 0 */
        !            63:       MPFR_SET_SAME_SIGN(y,x);
        !            64:       MPFR_RET(0);
        !            65:     }
        !            66:
        !            67:   /* General case */
        !            68:   {
        !            69:     /* Declaration of the intermediary variable */
        !            70:     mpfr_t te,t;
        !            71:
        !            72:     /* Declaration of the size variable */
        !            73:     mp_prec_t Nx = MPFR_PREC(x);   /* Precision of input variable */
        !            74:     mp_prec_t Ny = MPFR_PREC(y);   /* Precision of input variable */
        !            75:
        !            76:     mp_prec_t Nt;   /* Precision of the intermediary variable */
        !            77:     long int err;  /* Precision of error */
        !            78:
        !            79:     /* compute the precision of intermediary variable */
        !            80:     Nt=MAX(Nx,Ny);
        !            81:     /* the optimal number of bits : see algorithms.ps */
        !            82:     Nt=Nt+5+_mpfr_ceil_log2(Nt);
        !            83:
        !            84:     /* initialise of intermediary      variable */
        !            85:     mpfr_init(t);
        !            86:     mpfr_init(te);
        !            87:
        !            88:     /* First computation of cosh */
        !            89:     do {
        !            90:
        !            91:       /* reactualisation of the precision */
        !            92:       mpfr_set_prec(t,Nt);
        !            93:       mpfr_set_prec(te,Nt);
        !            94:
        !            95:       /* compute expm1 */
        !            96:       mpfr_exp(te,x,GMP_RNDN);        /* exp(x)*/
        !            97:       mpfr_sub_ui(t,te,1,GMP_RNDN);   /* exp(x)-1 */
        !            98:
        !            99:       /* estimation of the error */
        !           100:       /*err=Nt-(_mpfr_ceil_log2(1+pow(2,MPFR_EXP(te)-MPFR_EXP(t))));*/
        !           101:       err=Nt-(MAX(MPFR_EXP(te)-MPFR_EXP(t),0)+1);
        !           102:
        !           103:       /* actualisation of the precision */
        !           104:       Nt += 10;
        !           105:
        !           106:     } while ((err <0) || !mpfr_can_round(t,err,GMP_RNDN,rnd_mode,Ny));
        !           107:
        !           108:       inexact = mpfr_set(y,t,rnd_mode);
        !           109:
        !           110:       mpfr_clear(t);
        !           111:       mpfr_clear(te);
        !           112:   }
        !           113:   return inexact;
        !           114: }