1 /* mpi-scan.c - MPI functions
2 * Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
3 *
4 * This file is part of GnuPG.
5 *
6 * GnuPG is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
10 *
11 * GnuPG is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
19 */
20
21 #include "mpi-internal.h"
22 #include "longlong.h"
23
24 /****************
25 * Scan through an mpi and return byte for byte. a -1 is returned to indicate
26 * the end of the mpi. Scanning is done from the lsb to the msb, returned
27 * values are in the range of 0 .. 255.
28 *
29 * FIXME: This code is VERY ugly!
30 */
mpi_getbyte(const MPI a,unsigned idx)31 int mpi_getbyte(const MPI a, unsigned idx)
32 {
33 int i, j;
34 unsigned n;
35 mpi_ptr_t ap;
36 mpi_limb_t limb;
37
38 ap = a->d;
39 for (n = 0, i = 0; i < a->nlimbs; i++) {
40 limb = ap[i];
41 for (j = 0; j < BYTES_PER_MPI_LIMB; j++, n++)
42 if (n == idx)
43 return (limb >> j * 8) & 0xff;
44 }
45 return -1;
46 }
47
48 /****************
49 * Put a value at position IDX into A. idx counts from lsb to msb
50 */
mpi_putbyte(MPI a,unsigned idx,int xc)51 void mpi_putbyte(MPI a, unsigned idx, int xc)
52 {
53 int i, j;
54 unsigned n;
55 mpi_ptr_t ap;
56 mpi_limb_t limb, c;
57
58 c = xc & 0xff;
59 ap = a->d;
60 for (n = 0, i = 0; i < a->alloced; i++) {
61 limb = ap[i];
62 for (j = 0; j < BYTES_PER_MPI_LIMB; j++, n++)
63 if (n == idx) {
64 #if BYTES_PER_MPI_LIMB == 4
65 if (j == 0)
66 limb = (limb & 0xffffff00) | c;
67 else if (j == 1)
68 limb = (limb & 0xffff00ff) | (c << 8);
69 else if (j == 2)
70 limb = (limb & 0xff00ffff) | (c << 16);
71 else
72 limb = (limb & 0x00ffffff) | (c << 24);
73 #elif BYTES_PER_MPI_LIMB == 8
74 if (j == 0)
75 limb = (limb & 0xffffffffffffff00) | c;
76 else if (j == 1)
77 limb =
78 (limb & 0xffffffffffff00ff) | (c <<
79 8);
80 else if (j == 2)
81 limb =
82 (limb & 0xffffffffff00ffff) | (c <<
83 16);
84 else if (j == 3)
85 limb =
86 (limb & 0xffffffff00ffffff) | (c <<
87 24);
88 else if (j == 4)
89 limb =
90 (limb & 0xffffff00ffffffff) | (c <<
91 32);
92 else if (j == 5)
93 limb =
94 (limb & 0xffff00ffffffffff) | (c <<
95 40);
96 else if (j == 6)
97 limb =
98 (limb & 0xff00ffffffffffff) | (c <<
99 48);
100 else
101 limb =
102 (limb & 0x00ffffffffffffff) | (c <<
103 56);
104 #else
105 #error please enhance this function, its ugly - i know.
106 #endif
107 if (a->nlimbs <= i)
108 a->nlimbs = i + 1;
109 ap[i] = limb;
110 return;
111 }
112 }
113 log_bug("index out of range\n");
114 }
115
116 /****************
117 * Count the number of zerobits at the low end of A
118 */
mpi_trailing_zeros(const MPI a)119 unsigned mpi_trailing_zeros(const MPI a)
120 {
121 unsigned n, count = 0;
122
123 for (n = 0; n < a->nlimbs; n++) {
124 if (a->d[n]) {
125 unsigned nn;
126 mpi_limb_t alimb = a->d[n];
127
128 count_trailing_zeros(nn, alimb);
129 count += nn;
130 break;
131 }
132 count += BITS_PER_MPI_LIMB;
133 }
134 return count;
135
136 }
137