Return to log1p.c CVS log

Up to [local] / OpenXM_contrib / gmp / mpfr

Annotation of OpenXM_contrib/gmp/mpfr/log1p.c, Revision 1.1.1.1

1.1       ohara       1: /* mpfr_log1p -- Compute log(1+x)
                      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:  /* The computation of log1p is done by
                     28:
                     29:     log1p(x)=log(1+x)
                     30:  */
                     31:
                     32: int
                     33: mpfr_log1p (mpfr_ptr y, mpfr_srcptr x, mp_rnd_t rnd_mode)
                     34: {
                     35:   int comp, 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 (result is not defined) */
                     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:           MPFR_RET(0);
                     53:         }
                     54:       else
                     55:         {
                     56:           MPFR_SET_NAN(y);
                     57:           MPFR_RET_NAN;
                     58:         }
                     59:     }
                     60:
                     61:   comp = mpfr_cmp_si(x,-1);
                     62:   /* x<-1 undefined */
                     63:   if (comp < 0)
                     64:     {
                     65:       MPFR_SET_NAN(y);
                     66:       MPFR_RET_NAN;
                     67:     }
                     68:   /* x=0: log1p(-1)=-inf (division by zero) */
                     69:   if (comp == 0)
                     70:     {
                     71:       MPFR_SET_INF(y);
                     72:       MPFR_SET_POS(y);
                     73:       MPFR_RET_NAN;
                     74:     }
                     75:
                     76:   MPFR_CLEAR_INF(y);
                     77:
                     78:   if (MPFR_IS_ZERO(x))
                     79:     {
                     80:       MPFR_SET_ZERO(y);   /* log1p(+/- 0) = +/- 0 */
                     81:       MPFR_SET_SAME_SIGN(y, x);
                     82:       MPFR_RET(0);
                     83:     }
                     84:
                     85:   /* General case */
                     86:   {
                     87:     /* Declaration of the intermediary variable */
                     88:     mpfr_t t;
                     89:
                     90:     /* Declaration of the size variable */
                     91:     mp_prec_t Nx = MPFR_PREC(x);   /* Precision of input variable */
                     92:     mp_prec_t Ny = MPFR_PREC(y);   /* Precision of input variable */
                     93:
                     94:     mp_prec_t Nt;   /* Precision of the intermediary variable */
                     95:     long int err;  /* Precision of error */
                     96:
                     97:     /* compute the precision of intermediary variable */
                     98:     Nt=MAX(Nx,Ny);
                     99:     /* the optimal number of bits : see algorithms.ps */
                    100:     Nt=Nt+5+_mpfr_ceil_log2(Nt);
                    101:
                    102:     /* initialise of intermediary variable */
                    103:     mpfr_init(t);
                    104:
                    105:     /* First computation of cosh */
                    106:     do {
                    107:
                    108:       /* reactualisation of the precision */
                    109:       mpfr_set_prec(t, Nt);
                    110:
                    111:       /* compute log1p */
                    112:       mpfr_add_ui (t, x, 1, GMP_RNDN);   /* 1+x */
                    113:       mpfr_log (t, t, GMP_RNDN);        /* log(1+x)*/
                    114:
                    115:       /* estimation of the error */
                    116:       /*err=Nt-(_mpfr_ceil_log2(1+pow(2,1-MPFR_EXP(t))));*/
                    117:       err=Nt-(MAX(1-MPFR_EXP(t),0)+1);
                    118:
                    119:       /* actualisation of the precision */
                    120:       Nt += 10;
                    121:
                    122:     } while ((err<0) || !mpfr_can_round(t, err, GMP_RNDN, rnd_mode, Ny));
                    123:
                    124:     inexact = mpfr_set (y, t, rnd_mode);
                    125:
                    126:     mpfr_clear(t);
                    127:   }
                    128:   return inexact;
                    129: }