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Annotation of OpenXM_contrib/gmp/mpfr/expm1.c, Revision 1.1.1.1

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: }