1 /* mpz_cdiv_r_2exp, mpz_fdiv_r_2exp -- remainder from mpz divided by 2^n.
2
3 Copyright 2001, 2002, 2004, 2012 Free Software Foundation, Inc.
4
5 This file is part of the GNU MP Library.
6
7 The GNU MP Library is free software; you can redistribute it and/or modify
8 it under the terms of either:
9
10 * the GNU Lesser General Public License as published by the Free
11 Software Foundation; either version 3 of the License, or (at your
12 option) any later version.
13
14 or
15
16 * the GNU General Public License as published by the Free Software
17 Foundation; either version 2 of the License, or (at your option) any
18 later version.
19
20 or both in parallel, as here.
21
22 The GNU MP Library is distributed in the hope that it will be useful, but
23 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
24 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
25 for more details.
26
27 You should have received copies of the GNU General Public License and the
28 GNU Lesser General Public License along with the GNU MP Library. If not,
29 see https://www.gnu.org/licenses/. */
30
31 #include "gmp-impl.h"
32
33
34 /* Bit mask of "n" least significant bits of a limb. */
35 #define LOW_MASK(n) ((CNST_LIMB(1) << (n)) - 1)
36
37
38 /* dir==1 for ceil, dir==-1 for floor */
39
40 static void __gmpz_cfdiv_r_2exp (REGPARM_3_1 (mpz_ptr, mpz_srcptr, mp_bitcnt_t, int)) REGPARM_ATTR (1);
41 #define cfdiv_r_2exp(w,u,cnt,dir) __gmpz_cfdiv_r_2exp (REGPARM_3_1 (w, u, cnt, dir))
42
43 REGPARM_ATTR (1) static void
44 cfdiv_r_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt, int dir)
45 {
46 mp_size_t usize, abs_usize, limb_cnt, i;
47 mp_srcptr up;
48 mp_ptr wp;
49 mp_limb_t high;
50
51 usize = SIZ(u);
52 if (usize == 0)
53 {
54 SIZ(w) = 0;
55 return;
56 }
57
58 limb_cnt = cnt / GMP_NUMB_BITS;
59 cnt %= GMP_NUMB_BITS;
60 abs_usize = ABS (usize);
61
62 /* MPZ_REALLOC(w) below is only when w!=u, so we can fetch PTR(u) here
63 nice and early */
64 up = PTR(u);
65
66 if ((usize ^ dir) < 0)
67 {
68 /* Round towards zero, means just truncate */
69
70 if (w == u)
71 {
72 /* if already smaller than limb_cnt then do nothing */
73 if (abs_usize <= limb_cnt)
74 return;
75 wp = (mp_ptr) up;
76 }
77 else
78 {
79 i = MIN (abs_usize, limb_cnt+1);
80 wp = MPZ_NEWALLOC (w, i);
81 MPN_COPY (wp, up, i);
82
83 /* if smaller than limb_cnt then only the copy is needed */
84 if (abs_usize <= limb_cnt)
85 {
86 SIZ(w) = usize;
87 return;
88 }
89 }
90 }
91 else
92 {
93 /* Round away from zero, means twos complement if non-zero */
94
95 /* if u!=0 and smaller than divisor, then must negate */
96 if (abs_usize <= limb_cnt)
97 goto negate;
98
99 /* if non-zero low limb, then must negate */
100 for (i = 0; i < limb_cnt; i++)
101 if (up[i] != 0)
102 goto negate;
103
104 /* if non-zero partial limb, then must negate */
105 if ((up[limb_cnt] & LOW_MASK (cnt)) != 0)
106 goto negate;
107
108 /* otherwise low bits of u are zero, so that's the result */
109 SIZ(w) = 0;
110 return;
111
112 negate:
113 /* twos complement negation to get 2**cnt-u */
114
115 wp = MPZ_REALLOC (w, limb_cnt+1);
116 up = PTR(u);
117
118 /* Ones complement */
119 i = MIN (abs_usize, limb_cnt+1);
120 ASSERT_CARRY (mpn_neg (wp, up, i));
121 for ( ; i <= limb_cnt; i++)
122 wp[i] = GMP_NUMB_MAX;
123
124 usize = -usize;
125 }
126
127 /* Mask the high limb */
128 high = wp[limb_cnt];
129 high &= LOW_MASK (cnt);
130 wp[limb_cnt] = high;
131
132 /* Strip any consequent high zeros */
133 while (high == 0)
134 {
135 limb_cnt--;
136 if (limb_cnt < 0)
137 {
138 SIZ(w) = 0;
139 return;
140 }
141 high = wp[limb_cnt];
142 }
143
144 limb_cnt++;
145 SIZ(w) = (usize >= 0 ? limb_cnt : -limb_cnt);
146 }
147
148
149 void
150 mpz_cdiv_r_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt)
151 {
152 cfdiv_r_2exp (w, u, cnt, 1);
153 }
154
155 void
156 mpz_fdiv_r_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt)
157 {
158 cfdiv_r_2exp (w, u, cnt, -1);
159 }