1 /* mpfr_cache -- cache interface for multiple-precision constants in MPFR.
2
3 Copyright 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc.
4 Contributed by the AriC and Caramel projects, INRIA.
5
6 This file is part of the GNU MPFR Library.
7
8 The GNU MPFR Library is free software; you can redistribute it and/or modify
9 it under the terms of the GNU Lesser General Public License as published by
10 the Free Software Foundation; either version 3 of the License, or (at your
11 option) any later version.
12
13 The GNU MPFR Library is distributed in the hope that it will be useful, but
14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
15 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
16 License for more details.
17
18 You should have received a copy of the GNU Lesser General Public License
19 along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see
20 http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
21 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
22
23 #include "mpfr-impl.h"
24
25 #if 0 /* this function is not used/documented/tested so far, it could be
26 useful if some user wants to add a new constant to mpfr, and
27 implement a cache mechanism for that constant */
28 void
29 mpfr_init_cache (mpfr_cache_t cache, int (*func)(mpfr_ptr, mpfr_rnd_t))
30 {
31 MPFR_PREC (cache->x) = 0; /* Invalid prec to detect that the cache is not
32 valid. Maybe add a flag? */
33 cache->func = func;
34 }
35 #endif
36
37 void
mpfr_clear_cache(mpfr_cache_t cache)38 mpfr_clear_cache (mpfr_cache_t cache)
39 {
40 if (MPFR_PREC (cache->x) != 0)
41 mpfr_clear (cache->x);
42 MPFR_PREC (cache->x) = 0;
43 }
44
45 int
mpfr_cache(mpfr_ptr dest,mpfr_cache_t cache,mpfr_rnd_t rnd)46 mpfr_cache (mpfr_ptr dest, mpfr_cache_t cache, mpfr_rnd_t rnd)
47 {
48 mpfr_prec_t prec = MPFR_PREC (dest);
49 mpfr_prec_t pold = MPFR_PREC (cache->x);
50 int inexact, sign;
51 MPFR_SAVE_EXPO_DECL (expo);
52
53 MPFR_SAVE_EXPO_MARK (expo);
54
55 if (MPFR_UNLIKELY (prec > pold))
56 {
57 /* No previous result in the cache or the precision of the
58 previous result is not sufficient. */
59
60 if (MPFR_UNLIKELY (pold == 0)) /* No previous result. */
61 mpfr_init2 (cache->x, prec);
62
63 /* Update the cache. */
64 pold = prec;
65 /* no need to keep the previous value */
66 mpfr_set_prec (cache->x, pold);
67 cache->inexact = (*cache->func) (cache->x, MPFR_RNDN);
68 }
69
70 /* now pold >= prec is the precision of cache->x */
71
72 /* First, check if the cache has the exact value (unlikely).
73 Else the exact value is between (assuming x=cache->x > 0):
74 x and x+ulp(x) if cache->inexact < 0,
75 x-ulp(x) and x if cache->inexact > 0,
76 and abs(x-exact) <= ulp(x)/2. */
77
78 /* we assume all cached constants are positive */
79 MPFR_ASSERTN (MPFR_IS_POS (cache->x)); /* TODO... */
80 sign = MPFR_SIGN (cache->x);
81 MPFR_SET_EXP (dest, MPFR_GET_EXP (cache->x));
82 MPFR_SET_SIGN (dest, sign);
83
84 /* round cache->x from precision pold down to precision prec */
85 MPFR_RNDRAW_GEN (inexact, dest,
86 MPFR_MANT (cache->x), pold, rnd, sign,
87 if (MPFR_UNLIKELY (cache->inexact == 0))
88 {
89 if ((_sp[0] & _ulp) == 0)
90 {
91 inexact = -sign;
92 goto trunc_doit;
93 }
94 else
95 goto addoneulp;
96 }
97 else if (cache->inexact < 0)
98 goto addoneulp;
99 else /* cache->inexact > 0 */
100 {
101 inexact = -sign;
102 goto trunc_doit;
103 },
104 if (MPFR_UNLIKELY (++MPFR_EXP (dest) > __gmpfr_emax))
105 mpfr_overflow (dest, rnd, sign);
106 );
107
108 if (MPFR_LIKELY (cache->inexact != 0))
109 {
110 switch (rnd)
111 {
112 case MPFR_RNDZ:
113 case MPFR_RNDD:
114 if (MPFR_UNLIKELY (inexact == 0))
115 {
116 inexact = cache->inexact;
117 if (inexact > 0)
118 {
119 mpfr_nextbelow (dest);
120 inexact = -inexact;
121 }
122 }
123 break;
124 case MPFR_RNDU:
125 case MPFR_RNDA:
126 if (MPFR_UNLIKELY (inexact == 0))
127 {
128 inexact = cache->inexact;
129 if (inexact < 0)
130 {
131 mpfr_nextabove (dest);
132 inexact = -inexact;
133 }
134 }
135 break;
136 default: /* MPFR_RNDN */
137 if (MPFR_UNLIKELY(inexact == 0))
138 inexact = cache->inexact;
139 break;
140 }
141 }
142
143 MPFR_SAVE_EXPO_FREE (expo);
144 return mpfr_check_range (dest, inexact, rnd);
145 }
146