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