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1/* mpi-scan.c - MPI functions
2 *Copyright (C) 1998, 2001, 2002, 2003 Free Software Foundation, Inc.
3 *
4 * This file is part of Libgcrypt.
5 *
6 * Libgcrypt is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU Lesser General Public License as
8 * published by the Free Software Foundation; either version 2.1 of
9 * the License, or (at your option) any later version.
10 *
11 * Libgcrypt 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 Lesser General Public License for more details.
15 *
16 * You should have received a copy of the GNU Lesser General Public
17 * License 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 <config.h>
22#include <stdio.h>
23#include <stdlib.h>
24#include "mpi-internal.h"
25#include "longlong.h"
26
27/****************
28 * Scan through an mpi and return byte for byte. a -1 is returned to indicate
29 * the end of the mpi. Scanning is done from the lsb to the msb, returned
30 * values are in the range of 0 .. 255.
31 *
32 * FIXME: This code is VERY ugly!
33 */
34int
35_gcry_mpi_getbyte( gcry_mpi_t a, unsigned idx )
36{
37 int i, j;
38 unsigned n;
39 mpi_ptr_t ap;
40 mpi_limb_t limb;
41
42 ap = a->d;
43 for(n=0,i=0; i < a->nlimbs; i++ ) {
44 limb = ap[i];
45 for( j=0; j < BYTES_PER_MPI_LIMB; j++, n++ )
46 if( n == idx )
47 return (limb >> j*8) & 0xff;
48 }
49 return -1;
50}
51
52
53/****************
54 * Put a value at position IDX into A. idx counts from lsb to msb
55 */
56void
57_gcry_mpi_putbyte( gcry_mpi_t a, unsigned idx, int xc )
58{
59 int i, j;
60 unsigned n;
61 mpi_ptr_t ap;
62 mpi_limb_t limb, c;
63
64 c = xc & 0xff;
65 ap = a->d;
66 for(n=0,i=0; i < a->alloced; i++ ) {
67 limb = ap[i];
68 for( j=0; j < BYTES_PER_MPI_LIMB; j++, n++ )
69 if( n == idx ) {
70 #if BYTES_PER_MPI_LIMB == 4
71 if( j == 0 )
72 limb = (limb & 0xffffff00) | c;
73 else if( j == 1 )
74 limb = (limb & 0xffff00ff) | (c<<8);
75 else if( j == 2 )
76 limb = (limb & 0xff00ffff) | (c<<16);
77 else
78 limb = (limb & 0x00ffffff) | (c<<24);
79 #elif BYTES_PER_MPI_LIMB == 8
80 if( j == 0 )
81 limb = (limb & 0xffffffffffffff00) | c;
82 else if( j == 1 )
83 limb = (limb & 0xffffffffffff00ff) | (c<<8);
84 else if( j == 2 )
85 limb = (limb & 0xffffffffff00ffff) | (c<<16);
86 else if( j == 3 )
87 limb = (limb & 0xffffffff00ffffff) | (c<<24);
88 else if( j == 4 )
89 limb = (limb & 0xffffff00ffffffff) | (c<<32);
90 else if( j == 5 )
91 limb = (limb & 0xffff00ffffffffff) | (c<<40);
92 else if( j == 6 )
93 limb = (limb & 0xff00ffffffffffff) | (c<<48);
94 else
95 limb = (limb & 0x00ffffffffffffff) | (c<<56);
96 #else
97 #error please enhance this function, its ugly - i know.
98 #endif
99 if( a->nlimbs <= i )
100 a->nlimbs = i+1;
101 ap[i] = limb;
102 return;
103 }
104 }
105 abort(); /* index out of range */
106}
107
108
109/****************
110 * Count the number of zerobits at the low end of A
111 */
112unsigned
113_gcry_mpi_trailing_zeros( gcry_mpi_t a )
114{
115 unsigned n, count = 0;
116
117 for(n=0; n < a->nlimbs; n++ ) {
118 if( a->d[n] ) {
119 unsigned nn;
120 mpi_limb_t alimb = a->d[n];
121
122 count_trailing_zeros( nn, alimb );
123 count += nn;
124 break;
125 }
126 count += BITS_PER_MPI_LIMB;
127 }
128 return count;
129
130}
131
132