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