1/* mpz_cdiv_r_2exp, mpz_fdiv_r_2exp -- remainder from mpz divided by 2^n.
2
3Copyright 2001, 2002, 2004 Free Software Foundation, Inc.
4
5This file is part of the GNU MP Library.
6
7The GNU MP Library is free software; you can redistribute it and/or modify
8it under the terms of the GNU Lesser General Public License as published by
9the Free Software Foundation; either version 3 of the License, or (at your
10option) any later version.
11
12The GNU MP Library is distributed in the hope that it will be useful, but
13WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
14or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
15License for more details.
16
17You should have received a copy of the GNU Lesser General Public License
18along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
19
20#include "gmp.h"
21#include "gmp-impl.h"
22
23
24/* Bit mask of "n" least significant bits of a limb. */
25#define LOW_MASK(n)   ((CNST_LIMB(1) << (n)) - 1)
26
27
28/* dir==1 for ceil, dir==-1 for floor */
29
30static void __gmpz_cfdiv_r_2exp __GMP_PROTO ((REGPARM_3_1 (mpz_ptr, mpz_srcptr, mp_bitcnt_t, int))) REGPARM_ATTR (1);
31#define cfdiv_r_2exp(w,u,cnt,dir)  __gmpz_cfdiv_r_2exp (REGPARM_3_1 (w, u, cnt, dir))
32
33REGPARM_ATTR (1) static void
34cfdiv_r_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt, int dir)
35{
36  mp_size_t  usize, abs_usize, limb_cnt, i;
37  mp_srcptr  up;
38  mp_ptr     wp;
39  mp_limb_t  high;
40
41  usize = SIZ(u);
42  if (usize == 0)
43    {
44      SIZ(w) = 0;
45      return;
46    }
47
48  limb_cnt = cnt / GMP_NUMB_BITS;
49  cnt %= GMP_NUMB_BITS;
50  abs_usize = ABS (usize);
51
52  /* MPZ_REALLOC(w) below is only when w!=u, so we can fetch PTR(u) here
53     nice and early */
54  up = PTR(u);
55
56  if ((usize ^ dir) < 0)
57    {
58      /* Round towards zero, means just truncate */
59
60      if (w == u)
61        {
62          /* if already smaller than limb_cnt then do nothing */
63          if (abs_usize <= limb_cnt)
64            return;
65          wp = PTR(w);
66        }
67      else
68        {
69          i = MIN (abs_usize, limb_cnt+1);
70          MPZ_REALLOC (w, i);
71          wp = PTR(w);
72          MPN_COPY (wp, up, i);
73
74          /* if smaller than limb_cnt then only the copy is needed */
75          if (abs_usize <= limb_cnt)
76            {
77              SIZ(w) = usize;
78              return;
79            }
80        }
81    }
82  else
83    {
84      /* Round away from zero, means twos complement if non-zero */
85
86      /* if u!=0 and smaller than divisor, then must negate */
87      if (abs_usize <= limb_cnt)
88        goto negate;
89
90      /* if non-zero low limb, then must negate */
91      for (i = 0; i < limb_cnt; i++)
92        if (up[i] != 0)
93          goto negate;
94
95      /* if non-zero partial limb, then must negate */
96      if ((up[limb_cnt] & LOW_MASK (cnt)) != 0)
97        goto negate;
98
99      /* otherwise low bits of u are zero, so that's the result */
100      SIZ(w) = 0;
101      return;
102
103    negate:
104      /* twos complement negation to get 2**cnt-u */
105
106      MPZ_REALLOC (w, limb_cnt+1);
107      up = PTR(u);
108      wp = PTR(w);
109
110      /* Ones complement */
111      i = MIN (abs_usize, limb_cnt+1);
112      mpn_com (wp, up, i);
113      for ( ; i <= limb_cnt; i++)
114        wp[i] = GMP_NUMB_MAX;
115
116      /* Twos complement.  Since u!=0 in the relevant part, the twos
117         complement never gives 0 and a carry, so can use MPN_INCR_U. */
118      MPN_INCR_U (wp, limb_cnt+1, CNST_LIMB(1));
119
120      usize = -usize;
121    }
122
123  /* Mask the high limb */
124  high = wp[limb_cnt];
125  high &= LOW_MASK (cnt);
126  wp[limb_cnt] = high;
127
128  /* Strip any consequent high zeros */
129  while (high == 0)
130    {
131      limb_cnt--;
132      if (limb_cnt < 0)
133        {
134          SIZ(w) = 0;
135          return;
136        }
137      high = wp[limb_cnt];
138    }
139
140  limb_cnt++;
141  SIZ(w) = (usize >= 0 ? limb_cnt : -limb_cnt);
142}
143
144
145void
146mpz_cdiv_r_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt)
147{
148  cfdiv_r_2exp (w, u, cnt, 1);
149}
150
151void
152mpz_fdiv_r_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt)
153{
154  cfdiv_r_2exp (w, u, cnt, -1);
155}
156