Annotation of OpenXM_contrib/gmp/mpfr/log10.c, Revision 1.1.1.1
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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