1 /* mpfr_sub_ui -- subtract a floating-point number and a machine integer
2
3 Copyright 2000-2023 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
24 #define MPFR_NEED_LONGLONG_H
25 #include "mpfr-impl.h"
26
27 int
mpfr_sub_ui(mpfr_ptr y,mpfr_srcptr x,unsigned long int u,mpfr_rnd_t rnd_mode)28 mpfr_sub_ui (mpfr_ptr y, mpfr_srcptr x, unsigned long int u, mpfr_rnd_t rnd_mode)
29 {
30 MPFR_LOG_FUNC
31 (("x[%Pd]=%.*Rg u=%lu rnd=%d",
32 mpfr_get_prec(x), mpfr_log_prec, x, u, rnd_mode),
33 ("y[%Pd]=%.*Rg", mpfr_get_prec (y), mpfr_log_prec, y));
34
35 /* (unsigned long) 0 is assumed to be a real 0 (unsigned) */
36 if (MPFR_UNLIKELY (u == 0))
37 return mpfr_set (y, x, rnd_mode);
38
39 /* This block is actually useless, but this is a minor optimization. */
40 if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (x)))
41 {
42 if (MPFR_IS_NAN (x))
43 {
44 MPFR_SET_NAN (y);
45 MPFR_RET_NAN;
46 }
47 if (MPFR_IS_INF (x))
48 {
49 MPFR_SET_INF (y);
50 MPFR_SET_SAME_SIGN (y, x);
51 MPFR_RET (0); /* +/-infinity is exact */
52 }
53 /* The case x being zero is handled below: we can't use mpfr_set_si
54 as the opposite of u does not necessarily fit in a long. */
55 }
56
57 /* Main code */
58 {
59 int inex;
60 MPFR_SAVE_EXPO_DECL (expo);
61
62 /* Optimization note: Exponent save/restore operations may be
63 removed if mpfr_sub works even when uu is out-of-range. */
64 MPFR_SAVE_EXPO_MARK (expo);
65
66 #ifdef MPFR_LONG_WITHIN_LIMB
67 {
68 mpfr_t uu;
69 mp_limb_t up[1];
70 int cnt;
71
72 MPFR_TMP_INIT1 (up, uu, GMP_NUMB_BITS);
73 /* So, u fits in a mp_limb_t, which justifies the casts below. */
74 MPFR_ASSERTD (u != 0);
75 count_leading_zeros (cnt, (mp_limb_t) u);
76 up[0] = (mp_limb_t) u << cnt;
77 MPFR_SET_EXP (uu, GMP_NUMB_BITS - cnt);
78 inex = mpfr_sub (y, x, uu, rnd_mode);
79 }
80 #else
81 {
82 mpfr_t uu;
83
84 mpfr_init2 (uu, sizeof (unsigned long) * CHAR_BIT);
85 mpfr_set_ui (uu, u, MPFR_RNDZ);
86 inex = mpfr_sub (y, x, uu, rnd_mode);
87 mpfr_clear (uu);
88 }
89 #endif
90
91 MPFR_SAVE_EXPO_UPDATE_FLAGS (expo, __gmpfr_flags);
92 MPFR_SAVE_EXPO_FREE (expo);
93 return mpfr_check_range (y, inex, rnd_mode);
94 }
95 }
96