1/* mpfr_fits_*_p -- test whether an mpfr fits a C signed type.
2
3Copyright 2003-2023 Free Software Foundation, Inc.
4Contributed by the AriC and Caramba projects, INRIA.
5
6This file is part of the GNU MPFR Library.
7
8The GNU MPFR Library is free software; you can redistribute it and/or modify
9it under the terms of the GNU Lesser General Public License as published by
10the Free Software Foundation; either version 3 of the License, or (at your
11option) any later version.
12
13The GNU MPFR Library is distributed in the hope that it will be useful, but
14WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
15or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
16License for more details.
17
18You should have received a copy of the GNU Lesser General Public License
19along with the GNU MPFR Library; see the file COPYING.LESSER.  If not, see
20https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
2151 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
22
23#include "mpfr-impl.h"
24
25/* The original version of this file came from GMP's mpf/fits_s.h;
26   it has been adapted for MPFR.  In particular, the result can be
27   rounded away from zero. */
28
29int
30FUNCTION (mpfr_srcptr f, mpfr_rnd_t rnd)
31{
32  mpfr_flags_t saved_flags;
33  mpfr_exp_t e;
34  int prec;
35  mpfr_t x;
36  int neg;
37  int res;
38
39  if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (f)))
40    /* Zero always fit */
41    return MPFR_IS_ZERO (f) ? 1 : 0;
42
43  /* now it fits if either
44     (a) MINIMUM <= f <= MAXIMUM
45     (b) or MINIMUM <= round(f, prec(slong), rnd) <= MAXIMUM */
46
47  e = MPFR_GET_EXP (f);
48  if (e < 1)
49    return 1; /* |f| < 1: always fits */
50
51  neg = MPFR_IS_NEG (f);
52
53  /* let EXTREMUM be MAXIMUM if f > 0, and MINIMUM if f < 0 */
54
55  /* first compute prec(EXTREMUM), this could be done at configure time,
56     but the result can depend on neg (the loop is moved inside the "if"
57     to give the compiler a better chance to compute prec statically) */
58  if (neg)
59    {
60      unsigned TYPE s;
61      /* In C90, the division on negative integers isn't well-defined. */
62      s = SAFE_ABS (unsigned TYPE, MINIMUM);
63      for (prec = 0; s != 0; s /= 2, prec ++);
64    }
65  else
66    {
67      TYPE s;
68      s = MAXIMUM;
69      for (prec = 0; s != 0; s /= 2, prec ++);
70    }
71
72  /* EXTREMUM needs prec bits, i.e. 2^(prec-1) <= |EXTREMUM| < 2^prec */
73
74   /* if e <= prec - 1, then f < 2^(prec-1) <= |EXTREMUM| */
75  if (e <= prec - 1)
76    return 1;
77
78  /* if e >= prec + 1, then f >= 2^prec > |EXTREMUM| */
79  if (e >= prec + 1)
80    return 0;
81
82  MPFR_ASSERTD (e == prec);
83
84  /* hard case: first round to prec bits, then check */
85  saved_flags = __gmpfr_flags;
86  mpfr_init2 (x, prec);
87  /* for RNDF, it suffices to check it fits when rounded away from zero */
88  mpfr_set (x, f, (rnd == MPFR_RNDF) ? MPFR_RNDA : rnd);
89  /* Warning! Due to the rounding, x can be an infinity. Here we use
90     the fact that singular numbers have a special exponent field,
91     thus well-defined and different from e, in which case this means
92     that the number does not fit. That's why we use MPFR_EXP, not
93     MPFR_GET_EXP. */
94  res = neg ? (mpfr_cmp_si (x, MINIMUM) >= 0) : (MPFR_EXP (x) == e);
95  mpfr_clear (x);
96  __gmpfr_flags = saved_flags;
97  return res;
98}
99