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7e8dec91 DK |
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 | */ | |
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 | */ | |
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 | */ | |
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 | } |