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.h"
32 #include "gmp-impl.h"
33
34
35 /* Bit mask of "n" least significant bits of a limb. */
36 #define LOW_MASK(n) ((CNST_LIMB(1) << (n)) - 1)
37
38
39 /* dir==1 for ceil, dir==-1 for floor */
40
41 static void __gmpz_cfdiv_r_2exp (REGPARM_3_1 (mpz_ptr, mpz_srcptr, mp_bitcnt_t, int)) REGPARM_ATTR (1);
42 #define cfdiv_r_2exp(w,u,cnt,dir) __gmpz_cfdiv_r_2exp (REGPARM_3_1 (w, u, cnt, dir))
43
44 REGPARM_ATTR (1) static void
cfdiv_r_2exp(mpz_ptr w,mpz_srcptr u,mp_bitcnt_t cnt,int dir)45 cfdiv_r_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt, int dir)
46 {
47 mp_size_t usize, abs_usize, limb_cnt, i;
48 mp_srcptr up;
49 mp_ptr wp;
50 mp_limb_t high;
51
52 usize = SIZ(u);
53 if (usize == 0)
54 {
55 SIZ(w) = 0;
56 return;
57 }
58
59 limb_cnt = cnt / GMP_NUMB_BITS;
60 cnt %= GMP_NUMB_BITS;
61 abs_usize = ABS (usize);
62
63 /* MPZ_REALLOC(w) below is only when w!=u, so we can fetch PTR(u) here
64 nice and early */
65 up = PTR(u);
66
67 if ((usize ^ dir) < 0)
68 {
69 /* Round towards zero, means just truncate */
70
71 if (w == u)
72 {
73 /* if already smaller than limb_cnt then do nothing */
74 if (abs_usize <= limb_cnt)
75 return;
76 wp = PTR(w);
77 }
78 else
79 {
80 i = MIN (abs_usize, limb_cnt+1);
81 wp = MPZ_REALLOC (w, i);
82 MPN_COPY (wp, up, i);
83
84 /* if smaller than limb_cnt then only the copy is needed */
85 if (abs_usize <= limb_cnt)
86 {
87 SIZ(w) = usize;
88 return;
89 }
90 }
91 }
92 else
93 {
94 /* Round away from zero, means twos complement if non-zero */
95
96 /* if u!=0 and smaller than divisor, then must negate */
97 if (abs_usize <= limb_cnt)
98 goto negate;
99
100 /* if non-zero low limb, then must negate */
101 for (i = 0; i < limb_cnt; i++)
102 if (up[i] != 0)
103 goto negate;
104
105 /* if non-zero partial limb, then must negate */
106 if ((up[limb_cnt] & LOW_MASK (cnt)) != 0)
107 goto negate;
108
109 /* otherwise low bits of u are zero, so that's the result */
110 SIZ(w) = 0;
111 return;
112
113 negate:
114 /* twos complement negation to get 2**cnt-u */
115
116 wp = MPZ_REALLOC (w, limb_cnt+1);
117 up = PTR(u);
118
119 /* Ones complement */
120 i = MIN (abs_usize, limb_cnt+1);
121 mpn_com (wp, up, i);
122 for ( ; i <= limb_cnt; i++)
123 wp[i] = GMP_NUMB_MAX;
124
125 /* Twos complement. Since u!=0 in the relevant part, the twos
126 complement never gives 0 and a carry, so can use MPN_INCR_U. */
127 MPN_INCR_U (wp, limb_cnt+1, CNST_LIMB(1));
128
129 usize = -usize;
130 }
131
132 /* Mask the high limb */
133 high = wp[limb_cnt];
134 high &= LOW_MASK (cnt);
135 wp[limb_cnt] = high;
136
137 /* Strip any consequent high zeros */
138 while (high == 0)
139 {
140 limb_cnt--;
141 if (limb_cnt < 0)
142 {
143 SIZ(w) = 0;
144 return;
145 }
146 high = wp[limb_cnt];
147 }
148
149 limb_cnt++;
150 SIZ(w) = (usize >= 0 ? limb_cnt : -limb_cnt);
151 }
152
153
154 void
mpz_cdiv_r_2exp(mpz_ptr w,mpz_srcptr u,mp_bitcnt_t cnt)155 mpz_cdiv_r_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt)
156 {
157 cfdiv_r_2exp (w, u, cnt, 1);
158 }
159
160 void
mpz_fdiv_r_2exp(mpz_ptr w,mpz_srcptr u,mp_bitcnt_t cnt)161 mpz_fdiv_r_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt)
162 {
163 cfdiv_r_2exp (w, u, cnt, -1);
164 }
165