mpi-scan.c
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/* mpi-scan.c - MPI functions
* Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
*
* This file is part of GnuPG.
*
* GnuPG is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* GnuPG is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
*/
#include "mpi-internal.h"
#include "longlong.h"
/****************
* Scan through an mpi and return byte for byte. a -1 is returned to indicate
* the end of the mpi. Scanning is done from the lsb to the msb, returned
* values are in the range of 0 .. 255.
*
* FIXME: This code is VERY ugly!
*/
int mpi_getbyte(const MPI a, unsigned idx)
{
int i, j;
unsigned n;
mpi_ptr_t ap;
mpi_limb_t limb;
ap = a->d;
for (n = 0, i = 0; i < a->nlimbs; i++) {
limb = ap[i];
for (j = 0; j < BYTES_PER_MPI_LIMB; j++, n++)
if (n == idx)
return (limb >> j * 8) & 0xff;
}
return -1;
}
/****************
* Put a value at position IDX into A. idx counts from lsb to msb
*/
void mpi_putbyte(MPI a, unsigned idx, int xc)
{
int i, j;
unsigned n;
mpi_ptr_t ap;
mpi_limb_t limb, c;
c = xc & 0xff;
ap = a->d;
for (n = 0, i = 0; i < a->alloced; i++) {
limb = ap[i];
for (j = 0; j < BYTES_PER_MPI_LIMB; j++, n++)
if (n == idx) {
#if BYTES_PER_MPI_LIMB == 4
if (j == 0)
limb = (limb & 0xffffff00) | c;
else if (j == 1)
limb = (limb & 0xffff00ff) | (c << 8);
else if (j == 2)
limb = (limb & 0xff00ffff) | (c << 16);
else
limb = (limb & 0x00ffffff) | (c << 24);
#elif BYTES_PER_MPI_LIMB == 8
if (j == 0)
limb = (limb & 0xffffffffffffff00) | c;
else if (j == 1)
limb =
(limb & 0xffffffffffff00ff) | (c <<
8);
else if (j == 2)
limb =
(limb & 0xffffffffff00ffff) | (c <<
16);
else if (j == 3)
limb =
(limb & 0xffffffff00ffffff) | (c <<
24);
else if (j == 4)
limb =
(limb & 0xffffff00ffffffff) | (c <<
32);
else if (j == 5)
limb =
(limb & 0xffff00ffffffffff) | (c <<
40);
else if (j == 6)
limb =
(limb & 0xff00ffffffffffff) | (c <<
48);
else
limb =
(limb & 0x00ffffffffffffff) | (c <<
56);
#else
#error please enhance this function, its ugly - i know.
#endif
if (a->nlimbs <= i)
a->nlimbs = i + 1;
ap[i] = limb;
return;
}
}
log_bug("index out of range\n");
}
/****************
* Count the number of zerobits at the low end of A
*/
unsigned mpi_trailing_zeros(const MPI a)
{
unsigned n, count = 0;
for (n = 0; n < a->nlimbs; n++) {
if (a->d[n]) {
unsigned nn;
mpi_limb_t alimb = a->d[n];
count_trailing_zeros(nn, alimb);
count += nn;
break;
}
count += BITS_PER_MPI_LIMB;
}
return count;
}