1 /* mpn_sec_div_qr, mpn_sec_div_r -- Compute Q = floor(U / V), U = U mod V.
2 Side-channel silent under the assumption that the used instructions are
3 side-channel silent.
4
5 Contributed to the GNU project by Torbjörn Granlund.
6
7 Copyright 2011-2015 Free Software Foundation, Inc.
8
9 This file is part of the GNU MP Library.
10
11 The GNU MP Library is free software; you can redistribute it and/or modify
12 it under the terms of either:
13
14 * the GNU Lesser General Public License as published by the Free
15 Software Foundation; either version 3 of the License, or (at your
16 option) any later version.
17
18 or
19
20 * the GNU General Public License as published by the Free Software
21 Foundation; either version 2 of the License, or (at your option) any
22 later version.
23
24 or both in parallel, as here.
25
26 The GNU MP Library is distributed in the hope that it will be useful, but
27 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
28 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
29 for more details.
30
31 You should have received copies of the GNU General Public License and the
32 GNU Lesser General Public License along with the GNU MP Library. If not,
33 see https://www.gnu.org/licenses/. */
34
35 #include "gmp-impl.h"
36 #include "longlong.h"
37
38 #if OPERATION_sec_div_qr
39 #define FNAME mpn_sec_div_qr
40 #define FNAME_itch mpn_sec_div_qr_itch
41 #define Q(q) q,
42 #define RETTYPE mp_limb_t
43 #endif
44 #if OPERATION_sec_div_r
45 #define FNAME mpn_sec_div_r
46 #define FNAME_itch mpn_sec_div_r_itch
47 #define Q(q)
48 #define RETTYPE void
49 #endif
50
51 mp_size_t
FNAME_itch(mp_size_t nn,mp_size_t dn)52 FNAME_itch (mp_size_t nn, mp_size_t dn)
53 {
54 #if OPERATION_sec_div_qr
55 /* Needs (nn + dn + 1) + mpn_sec_pi1_div_qr's needs of (2nn' - dn + 1) for a
56 total of 3nn + 4 limbs at tp. Note that mpn_sec_pi1_div_qr's nn is one
57 greater than ours, therefore +4 and not just +2. */
58 return 3 * nn + 4;
59 #endif
60 #if OPERATION_sec_div_r
61 /* Needs (nn + dn + 1) + mpn_sec_pi1_div_r's needs of (dn + 1) for a total of
62 nn + 2dn + 2 limbs at tp. */
63 return nn + 2 * dn + 2;
64 #endif
65 }
66
67 RETTYPE
FNAME(Q (mp_ptr qp)mp_ptr np,mp_size_t nn,mp_srcptr dp,mp_size_t dn,mp_ptr tp)68 FNAME (Q(mp_ptr qp)
69 mp_ptr np, mp_size_t nn,
70 mp_srcptr dp, mp_size_t dn,
71 mp_ptr tp)
72 {
73 mp_limb_t d1, d0;
74 unsigned int cnt;
75 mp_limb_t inv32;
76
77 ASSERT (dn >= 1);
78 ASSERT (nn >= dn);
79 ASSERT (dp[dn - 1] != 0);
80
81 d1 = dp[dn - 1];
82 count_leading_zeros (cnt, d1);
83
84 if (cnt != 0)
85 {
86 mp_limb_t qh, cy;
87 mp_ptr np2, dp2;
88 dp2 = tp; /* dn limbs */
89 mpn_lshift (dp2, dp, dn, cnt);
90
91 np2 = tp + dn; /* (nn + 1) limbs */
92 cy = mpn_lshift (np2, np, nn, cnt);
93 np2[nn++] = cy;
94
95 d0 = dp2[dn - 1];
96 d0 += (~d0 != 0);
97 invert_limb (inv32, d0);
98
99 /* We add nn + dn to tp here, not nn + 1 + dn, as expected. This is
100 since nn here will have been incremented. */
101 #if OPERATION_sec_div_qr
102 qh = mpn_sec_pi1_div_qr (np2 + dn, np2, nn, dp2, dn, inv32, tp + nn + dn);
103 ASSERT (qh == 0); /* FIXME: this indicates inefficiency! */
104 MPN_COPY (qp, np2 + dn, nn - dn - 1);
105 qh = np2[nn - 1];
106 #else
107 mpn_sec_pi1_div_r (np2, nn, dp2, dn, inv32, tp + nn + dn);
108 #endif
109
110 mpn_rshift (np, np2, dn, cnt);
111
112 #if OPERATION_sec_div_qr
113 return qh;
114 #endif
115 }
116 else
117 {
118 /* FIXME: Consider copying np => np2 here, adding a 0-limb at the top.
119 That would simplify the underlying pi1 function, since then it could
120 assume nn > dn. */
121 d0 = dp[dn - 1];
122 d0 += (~d0 != 0);
123 invert_limb (inv32, d0);
124
125 #if OPERATION_sec_div_qr
126 return mpn_sec_pi1_div_qr (qp, np, nn, dp, dn, inv32, tp);
127 #else
128 mpn_sec_pi1_div_r (np, nn, dp, dn, inv32, tp);
129 #endif
130 }
131 }
132