mul_ui.c revision 1.1.1.4 
1/* mpfr_mul_ui -- multiply a floating-point number by a machine integer
2
3Copyright 1999-2020 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#define MPFR_NEED_LONGLONG_H
24#include "mpfr-impl.h"
25
26#undef mpfr_mul_ui
27MPFR_HOT_FUNCTION_ATTR int
28mpfr_mul_ui (mpfr_ptr y, mpfr_srcptr x, unsigned long int u, mpfr_rnd_t rnd_mode)
29{
30  int inexact;
31
32  if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (x)))
33    {
34      if (MPFR_IS_NAN (x))
35        {
36          MPFR_SET_NAN (y);
37          MPFR_RET_NAN;
38        }
39      else if (MPFR_IS_INF (x))
40        {
41          if (u != 0)
42            {
43              MPFR_SET_INF (y);
44              MPFR_SET_SAME_SIGN (y, x);
45              MPFR_RET (0); /* infinity is exact */
46            }
47          else /* 0 * infinity */
48            {
49              MPFR_SET_NAN (y);
50              MPFR_RET_NAN;
51            }
52        }
53      else /* x is zero */
54        {
55          MPFR_ASSERTD (MPFR_IS_ZERO (x));
56          MPFR_SET_ZERO (y);
57          MPFR_SET_SAME_SIGN (y, x);
58          MPFR_RET (0); /* zero is exact */
59        }
60    }
61  else if (u <= 1)
62    {
63      if (u < 1)
64        {
65          MPFR_SET_ZERO (y);
66          MPFR_SET_SAME_SIGN (y, x);
67          MPFR_RET (0); /* zero is exact */
68        }
69      else
70        return mpfr_set (y, x, rnd_mode);
71    }
72  else if (MPFR_UNLIKELY (IS_POW2 (u)))
73    return mpfr_mul_2si (y, x, MPFR_INT_CEIL_LOG2 (u), rnd_mode);
74
75#ifdef MPFR_LONG_WITHIN_LIMB
76  {
77    mp_limb_t *yp;
78    mp_size_t xn;
79    int cnt;
80    MPFR_TMP_DECL (marker);
81
82    yp = MPFR_MANT (y);
83    xn = MPFR_LIMB_SIZE (x);
84
85    MPFR_ASSERTD (xn < MP_SIZE_T_MAX);
86    MPFR_TMP_MARK(marker);
87    yp = MPFR_TMP_LIMBS_ALLOC (xn + 1);
88
89    MPFR_ASSERTN (u == (mp_limb_t) u);
90    yp[xn] = mpn_mul_1 (yp, MPFR_MANT (x), xn, u);
91
92    /* x * u is stored in yp[xn], ..., yp[0] */
93
94    /* since the case u=1 was treated above, we have u >= 2, thus
95       yp[xn] >= 1 since x was msb-normalized */
96    MPFR_ASSERTD (yp[xn] != 0);
97    if (MPFR_LIKELY (MPFR_LIMB_MSB (yp[xn]) == 0))
98      {
99        count_leading_zeros (cnt, yp[xn]);
100        mpn_lshift (yp, yp, xn + 1, cnt);
101      }
102    else
103      {
104        cnt = 0;
105      }
106
107    /* now yp[xn], ..., yp[0] is msb-normalized too, and has at most
108       PREC(x) + (GMP_NUMB_BITS - cnt) non-zero bits */
109    MPFR_RNDRAW (inexact, y, yp, (mpfr_prec_t) (xn + 1) * GMP_NUMB_BITS,
110                 rnd_mode, MPFR_SIGN (x), cnt -- );
111
112    MPFR_TMP_FREE (marker);
113
114    cnt = GMP_NUMB_BITS - cnt;
115    if (MPFR_UNLIKELY (__gmpfr_emax < MPFR_EMAX_MIN + cnt
116                       || MPFR_GET_EXP (x) > __gmpfr_emax - cnt))
117      return mpfr_overflow (y, rnd_mode, MPFR_SIGN(x));
118
119    MPFR_SET_EXP (y, MPFR_GET_EXP (x) + cnt);
120    MPFR_SET_SAME_SIGN (y, x);
121    MPFR_RET (inexact);
122  }
123#else
124  {
125    mpfr_t uu;
126    MPFR_SAVE_EXPO_DECL (expo);
127
128    mpfr_init2 (uu, sizeof (unsigned long) * CHAR_BIT);
129    /* Warning: u might be outside the current exponent range! */
130    MPFR_SAVE_EXPO_MARK (expo);
131    mpfr_set_ui (uu, u, MPFR_RNDZ);
132    inexact = mpfr_mul (y, x, uu, rnd_mode);
133    mpfr_clear (uu);
134    MPFR_SAVE_EXPO_UPDATE_FLAGS (expo, __gmpfr_flags);
135    MPFR_SAVE_EXPO_FREE (expo);
136    return mpfr_check_range (y, inexact, rnd_mode);
137  }
138#endif /* MPFR_LONG_WITHIN_LIMB */
139}
140