1 /* mpfr_fits_*_p -- test whether an mpfr fits a C unsigned type.
2
3 Copyright 2003-2023 Free Software Foundation, Inc.
4 Contributed by the AriC and Caramba 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 https://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 int
FUNCTION(mpfr_srcptr f,mpfr_rnd_t rnd)26 FUNCTION (mpfr_srcptr f, mpfr_rnd_t rnd)
27 {
28 mpfr_flags_t saved_flags;
29 mpfr_exp_t e;
30 int prec;
31 TYPE s;
32 mpfr_t x;
33 int res;
34
35 if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (f)))
36 return MPFR_IS_ZERO (f) ? 1 : 0; /* Zero always fits */
37
38 e = MPFR_GET_EXP (f);
39
40 if (MPFR_IS_NEG (f))
41 return e >= 1 ? 0 /* f <= -1 does not fit */
42 : rnd != MPFR_RNDN ? MPFR_IS_LIKE_RNDU (rnd, -1) /* directed mode */
43 : e < 0 ? 1 /* f > -1/2 fits in MPFR_RNDN */
44 : mpfr_powerof2_raw(f); /* -1/2 fits, -1 < f < -1/2 don't */
45
46 /* Now it fits if
47 (a) f <= MAXIMUM
48 (b) round(f, prec(slong), rnd) <= MAXIMUM */
49
50 /* first compute prec(MAXIMUM); fits in an int */
51 for (s = MAXIMUM, prec = 0; s != 0; s /= 2, prec ++);
52
53 /* MAXIMUM needs prec bits, i.e. MAXIMUM = 2^prec - 1 */
54
55 /* if e <= prec - 1, then f < 2^(prec-1) < MAXIMUM */
56 if (e <= prec - 1)
57 return 1;
58
59 /* if e >= prec + 1, then f >= 2^prec > MAXIMUM */
60 if (e >= prec + 1)
61 return 0;
62
63 MPFR_ASSERTD (e == prec);
64
65 /* hard case: first round to prec bits, then check */
66 saved_flags = __gmpfr_flags;
67 mpfr_init2 (x, prec);
68 /* For MPFR_RNDF, if f > 0 fits with RNDU, it will also fit with RNDD. */
69 mpfr_set (x, f, (rnd != MPFR_RNDF) ? rnd : MPFR_RNDU);
70 /* Warning! Due to the rounding, x can be an infinity. Here we use
71 the fact that singular numbers have a special exponent field,
72 thus well-defined and different from e, in which case this means
73 that the number does not fit. That's why we use MPFR_EXP, not
74 MPFR_GET_EXP. */
75 res = MPFR_EXP (x) == e;
76 mpfr_clear (x);
77 __gmpfr_flags = saved_flags;
78 return res;
79 }
80