1 /* ecc-mul-g.c
2
3 Copyright (C) 2013 Niels Möller
4
5 This file is part of GNU Nettle.
6
7 GNU Nettle is free software: you can redistribute it and/or
8 modify 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
17 Software Foundation; either version 2 of the License, or (at your
18 option) any later version.
19
20 or both in parallel, as here.
21
22 GNU Nettle is distributed in the hope that it will be useful,
23 but WITHOUT ANY WARRANTY; without even the implied warranty of
24 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
25 General Public License for more details.
26
27 You should have received copies of the GNU General Public License and
28 the GNU Lesser General Public License along with this program. If
29 not, see http://www.gnu.org/licenses/.
30 */
31
32 /* Development of Nettle's ECC support was funded by the .SE Internet Fund. */
33
34 #if HAVE_CONFIG_H
35 # include "config.h"
36 #endif
37
38 #include <assert.h>
39
40 #include "ecc.h"
41 #include "ecc-internal.h"
42
43 void
ecc_mul_g(const struct ecc_curve * ecc,mp_limb_t * r,const mp_limb_t * np,mp_limb_t * scratch)44 ecc_mul_g (const struct ecc_curve *ecc, mp_limb_t *r,
45 const mp_limb_t *np, mp_limb_t *scratch)
46 {
47 /* Scratch need determined by the ecc_add_jja call. Current total is
48 9 * ecc->p.size, at most 648 bytes. */
49 #define tp scratch
50 #define scratch_out (scratch + 3*ecc->p.size)
51
52 unsigned k, c;
53 unsigned i, j;
54 unsigned bit_rows;
55
56 int is_zero;
57
58 k = ecc->pippenger_k;
59 c = ecc->pippenger_c;
60
61 bit_rows = (ecc->p.bit_size + k - 1) / k;
62
63 mpn_zero (r, 3*ecc->p.size);
64
65 for (i = k, is_zero = 1; i-- > 0; )
66 {
67 ecc_dup_jj (ecc, r, r, scratch);
68 for (j = 0; j * c < bit_rows; j++)
69 {
70 unsigned bits;
71 /* Avoid the mp_bitcnt_t type for compatibility with older GMP
72 versions. */
73 unsigned bit_index;
74
75 /* Extract c bits from n, stride k, starting at i + kcj,
76 ending at i + k (cj + c - 1)*/
77 for (bits = 0, bit_index = i + k*(c*j+c); bit_index > i + k*c*j; )
78 {
79 mp_size_t limb_index;
80 unsigned shift;
81
82 bit_index -= k;
83
84 limb_index = bit_index / GMP_NUMB_BITS;
85 if (limb_index >= ecc->p.size)
86 continue;
87
88 shift = bit_index % GMP_NUMB_BITS;
89 bits = (bits << 1) | ((np[limb_index] >> shift) & 1);
90 }
91 sec_tabselect (tp, 2*ecc->p.size,
92 (ecc->pippenger_table
93 + (2*ecc->p.size * (mp_size_t) j << c)),
94 1<<c, bits);
95 cnd_copy (is_zero, r, tp, 2*ecc->p.size);
96 cnd_copy (is_zero, r + 2*ecc->p.size, ecc->unit, ecc->p.size);
97
98 ecc_add_jja (ecc, tp, r, tp, scratch_out);
99 /* Use the sum when valid. ecc_add_jja produced garbage if
100 is_zero != 0 or bits == 0, . */
101 cnd_copy (bits & (is_zero - 1), r, tp, 3*ecc->p.size);
102 is_zero &= (bits == 0);
103 }
104 }
105 #undef tp
106 #undef scratch_out
107 }
108