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: }
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