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Annotation of OpenXM_contrib/gmp/mpfr/log10.c, Revision 1.1

1.1     ! ohara       1: /* mpfr_log10 -- logarithm in base 10.
        !             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 <stdio.h>
        !            23: #include "gmp.h"
        !            24: #include "gmp-impl.h"
        !            25: #include "mpfr.h"
        !            26: #include "mpfr-impl.h"
        !            27:
        !            28:  /* The computation of r=log10(a)
        !            29:
        !            30:     r=log10(a)=log(a)/log(10)
        !            31:  */
        !            32:
        !            33: int
        !            34: mpfr_log10 (mpfr_ptr r, mpfr_srcptr a, mp_rnd_t rnd_mode)
        !            35: {
        !            36:   int inexact = 0;
        !            37:
        !            38:   /* If a is NaN, the result is NaN */
        !            39:   if (MPFR_IS_NAN(a))
        !            40:     {
        !            41:       MPFR_SET_NAN(r);
        !            42:       MPFR_RET_NAN;
        !            43:     }
        !            44:
        !            45:   MPFR_CLEAR_NAN(r);
        !            46:
        !            47:   /* check for infinity before zero */
        !            48:   if (MPFR_IS_INF(a))
        !            49:     {
        !            50:       if (MPFR_SIGN(a) < 0) /* log10(-Inf) = NaN */
        !            51:         {
        !            52:           MPFR_SET_NAN(r);
        !            53:           MPFR_RET_NAN;
        !            54:         }
        !            55:       else /* log10(+Inf) = +Inf */
        !            56:         {
        !            57:           MPFR_SET_INF(r);
        !            58:           MPFR_SET_POS(r);
        !            59:           MPFR_RET(0); /* exact */
        !            60:         }
        !            61:     }
        !            62:
        !            63:   /* Now we can clear the flags without damage even if r == a */
        !            64:   MPFR_CLEAR_INF(r);
        !            65:
        !            66:   if (MPFR_IS_ZERO(a))
        !            67:     {
        !            68:       MPFR_SET_INF(r);
        !            69:       MPFR_SET_NEG(r);
        !            70:       MPFR_RET(0); /* log10(0) is an exact -infinity */
        !            71:     }
        !            72:
        !            73:   /* If a is negative, the result is NaN */
        !            74:   if (MPFR_SIGN(a) < 0)
        !            75:     {
        !            76:       MPFR_SET_NAN(r);
        !            77:       MPFR_RET_NAN;
        !            78:     }
        !            79:
        !            80:   /* If a is 1, the result is 0 */
        !            81:   if (mpfr_cmp_ui (a, 1) == 0)
        !            82:     {
        !            83:       MPFR_SET_ZERO(r);
        !            84:       MPFR_SET_POS(r);
        !            85:       MPFR_RET(0); /* result is exact */
        !            86:     }
        !            87:
        !            88:   /* General case */
        !            89:   {
        !            90:     /* Declaration of the intermediary variable */
        !            91:     mpfr_t t, tt;
        !            92:     int ok;
        !            93:
        !            94:     /* Declaration of the size variable */
        !            95:     mp_prec_t Nx = MPFR_PREC(a);   /* Precision of input variable */
        !            96:     mp_prec_t Ny = MPFR_PREC(r);   /* Precision of output variable */
        !            97:
        !            98:     mp_prec_t Nt;   /* Precision of the intermediary variable */
        !            99:     long int err;  /* Precision of error */
        !           100:
        !           101:     /* compute the precision of intermediary variable */
        !           102:     Nt = MAX(Nx, Ny);
        !           103:     /* the optimal number of bits : see algorithms.ps */
        !           104:     Nt = Nt + 4+ _mpfr_ceil_log2 (Nt);
        !           105:
        !           106:     /* initialise of intermediary variables */
        !           107:     mpfr_init (t);
        !           108:     mpfr_init (tt);
        !           109:
        !           110:
        !           111:     /* First computation of log10 */
        !           112:     do {
        !           113:
        !           114:       /* reactualisation of the precision */
        !           115:       mpfr_set_prec (t, Nt);
        !           116:       mpfr_set_prec (tt, Nt);
        !           117:
        !           118:       /* compute log10 */
        !           119:       mpfr_set_ui (t, 10, GMP_RNDN);   /* 10 */
        !           120:       mpfr_log (t, t, GMP_RNDD);       /* log(10) */
        !           121:       mpfr_log (tt, a, GMP_RNDN);      /* log(a) */
        !           122:       mpfr_div (t, tt, t, GMP_RNDN);   /* log(a)/log(10) */
        !           123:
        !           124:       /* estimation of the error */
        !           125:       err = Nt - 4;
        !           126:
        !           127:       ok = mpfr_can_round (t, err, GMP_RNDN, rnd_mode, Ny);
        !           128:
        !           129:       /* log10(10^n) is exact */
        !           130:       if ((MPFR_SIGN(t) > 0) && mpfr_isinteger(t))
        !           131:         if (mpfr_ui_pow_ui (tt, 10, (unsigned long int) mpfr_get_d1 (t) + 0.5,
        !           132:                             GMP_RNDN) == 0)
        !           133:           if (mpfr_cmp (a, tt) == 0)
        !           134:             ok = 1;
        !           135:
        !           136:       /* actualisation of the precision */
        !           137:       Nt += 10;
        !           138:     } while ((err < 0) || !ok);
        !           139:
        !           140:     inexact = mpfr_set (r, t, rnd_mode);
        !           141:
        !           142:     mpfr_clear (t);
        !           143:     mpfr_clear (tt);
        !           144:   }
        !           145:
        !           146:   return inexact;
        !           147: }