1 /* mpn_remove -- divide out all multiples of odd mpn number from another mpn
2 number.
3
4 Contributed to the GNU project by Torbjorn Granlund.
5
6 THE FUNCTION IN THIS FILE IS INTERNAL WITH A MUTABLE INTERFACE. IT IS ONLY
7 SAFE TO REACH IT THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS ALMOST
8 GUARANTEED THAT IT WILL CHANGE OR DISAPPEAR IN A FUTURE GMP RELEASE.
9
10 Copyright 2009, 2012, 2013 Free Software Foundation, Inc.
11
12 This file is part of the GNU MP Library.
13
14 The GNU MP Library is free software; you can redistribute it and/or modify
15 it under the terms of either:
16
17 * the GNU Lesser General Public License as published by the Free
18 Software Foundation; either version 3 of the License, or (at your
19 option) any later version.
20
21 or
22
23 * the GNU General Public License as published by the Free Software
24 Foundation; either version 2 of the License, or (at your option) any
25 later version.
26
27 or both in parallel, as here.
28
29 The GNU MP Library is distributed in the hope that it will be useful, but
30 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
31 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
32 for more details.
33
34 You should have received copies of the GNU General Public License and the
35 GNU Lesser General Public License along with the GNU MP Library. If not,
36 see https://www.gnu.org/licenses/. */
37
38 #include "gmp.h"
39 #include "gmp-impl.h"
40
41 #if GMP_LIMB_BITS > 50
42 #define LOG 50
43 #else
44 #define LOG GMP_LIMB_BITS
45 #endif
46
47
48 /* Input: U = {up,un}, V = {vp,vn} must be odd, cap
49 Ouput W = {wp,*wn} allocation need is exactly *wn
50
51 Set W = U / V^k, where k is the largest integer <= cap such that the
52 division yields an integer.
53
54 FIXME: We currently allow any operand overlap. This is quite non mpn-ish
55 and might be changed, since it cost significant temporary space.
56 * If we require W to have space for un + 1 limbs, we could save qp or qp2
57 (but we will still need to copy things into wp 50% of the time).
58 * If we allow ourselves to clobber U, we could save the other of qp and qp2,
59 and the initial COPY (but also here we would need un + 1 limbs).
60 */
61
62 /* FIXME: We need to wrap mpn_bdiv_qr due to the itch interface. This need
63 indicates a flaw in the current itch mechanism: Which operands not greater
64 than un,un will incur the worst itch? We need a parallel foo_maxitch set
65 of functions. */
66 static void
mpn_bdiv_qr_wrap(mp_ptr qp,mp_ptr rp,mp_srcptr np,mp_size_t nn,mp_srcptr dp,mp_size_t dn)67 mpn_bdiv_qr_wrap (mp_ptr qp, mp_ptr rp,
68 mp_srcptr np, mp_size_t nn,
69 mp_srcptr dp, mp_size_t dn)
70 {
71 mp_ptr scratch_out;
72 TMP_DECL;
73
74 TMP_MARK;
75 scratch_out = TMP_ALLOC_LIMBS (mpn_bdiv_qr_itch (nn, dn));
76 mpn_bdiv_qr (qp, rp, np, nn, dp, dn, scratch_out);
77
78 TMP_FREE;
79 }
80
81 mp_bitcnt_t
mpn_remove(mp_ptr wp,mp_size_t * wn,mp_ptr up,mp_size_t un,mp_ptr vp,mp_size_t vn,mp_bitcnt_t cap)82 mpn_remove (mp_ptr wp, mp_size_t *wn,
83 mp_ptr up, mp_size_t un, mp_ptr vp, mp_size_t vn,
84 mp_bitcnt_t cap)
85 {
86 mp_ptr pwpsp[LOG];
87 mp_size_t pwpsn[LOG];
88 mp_size_t npowers;
89 mp_ptr tp, qp, np, pp, qp2;
90 mp_size_t pn, nn, qn, i;
91 mp_bitcnt_t pwr;
92 TMP_DECL;
93
94 ASSERT (un > 0);
95 ASSERT (vn > 0);
96 ASSERT (vp[0] % 2 != 0); /* 2-adic division wants odd numbers */
97 ASSERT (vn > 1 || vp[0] > 1); /* else we would loop indefinitely */
98
99 TMP_MARK;
100
101 tp = TMP_ALLOC_LIMBS ((un + 1 + vn) / 2); /* remainder */
102 qp = TMP_ALLOC_LIMBS (un + 1); /* quotient, alternating */
103 qp2 = TMP_ALLOC_LIMBS (un + 1); /* quotient, alternating */
104 pp = vp;
105 pn = vn;
106
107 MPN_COPY (qp, up, un);
108 qn = un;
109
110 npowers = 0;
111 while (qn >= pn)
112 {
113 qp[qn] = 0;
114 mpn_bdiv_qr_wrap (qp2, tp, qp, qn + 1, pp, pn);
115 if (!mpn_zero_p (tp, pn))
116 break; /* could not divide by V^npowers */
117
118 MP_PTR_SWAP (qp, qp2);
119 qn = qn - pn;
120 qn += qp[qn] != 0;
121
122 pwpsp[npowers] = pp;
123 pwpsn[npowers] = pn;
124 npowers++;
125
126 if (((mp_bitcnt_t) 2 << npowers) - 1 > cap)
127 break;
128
129 nn = 2 * pn - 1; /* next power will be at least this large */
130 if (nn > qn)
131 break; /* next power would be overlarge */
132
133 if (npowers == 1) /* Alloc once, but only if it's needed */
134 np = TMP_ALLOC_LIMBS (qn + LOG); /* powers of V */
135 else
136 np += pn;
137
138 mpn_sqr (np, pp, pn);
139 pn = nn + (np[nn] != 0);
140 pp = np;
141 }
142
143 pwr = ((mp_bitcnt_t) 1 << npowers) - 1;
144
145 for (i = npowers - 1; i >= 0; i--)
146 {
147 pn = pwpsn[i];
148 if (qn < pn)
149 continue;
150
151 if (pwr + ((mp_bitcnt_t) 1 << i) > cap)
152 continue; /* V^i would bring us past cap */
153
154 qp[qn] = 0;
155 mpn_bdiv_qr_wrap (qp2, tp, qp, qn + 1, pwpsp[i], pn);
156 if (!mpn_zero_p (tp, pn))
157 continue; /* could not divide by V^i */
158
159 MP_PTR_SWAP (qp, qp2);
160 qn = qn - pn;
161 qn += qp[qn] != 0;
162
163 pwr += (mp_bitcnt_t) 1 << i;
164 }
165
166 MPN_COPY (wp, qp, qn);
167 *wn = qn;
168
169 TMP_FREE;
170
171 return pwr;
172 }
173