309 lines
6.7 KiB
C
309 lines
6.7 KiB
C
/* mpi-bit.c - MPI bit level functions
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* Copyright (C) 1998, 1999 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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#define A_LIMB_1 ((mpi_limb_t) 1)
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/****************
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* Sometimes we have MSL (most significant limbs) which are 0;
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* this is for some reasons not good, so this function removes them.
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*/
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void mpi_normalize(MPI a)
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{
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for (; a->nlimbs && !a->d[a->nlimbs - 1]; a->nlimbs--)
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;
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}
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EXPORT_SYMBOL_GPL(mpi_normalize);
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/****************
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* Return the number of bits in A.
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*/
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unsigned mpi_get_nbits(MPI a)
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{
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unsigned n;
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mpi_normalize(a);
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if (a->nlimbs) {
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mpi_limb_t alimb = a->d[a->nlimbs - 1];
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if (alimb)
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n = count_leading_zeros(alimb);
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else
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n = BITS_PER_MPI_LIMB;
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n = BITS_PER_MPI_LIMB - n + (a->nlimbs - 1) * BITS_PER_MPI_LIMB;
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} else
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n = 0;
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return n;
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}
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EXPORT_SYMBOL_GPL(mpi_get_nbits);
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/****************
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* Test whether bit N is set.
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*/
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int mpi_test_bit(MPI a, unsigned int n)
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{
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unsigned int limbno, bitno;
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mpi_limb_t limb;
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limbno = n / BITS_PER_MPI_LIMB;
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bitno = n % BITS_PER_MPI_LIMB;
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if (limbno >= a->nlimbs)
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return 0; /* too far left: this is a 0 */
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limb = a->d[limbno];
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return (limb & (A_LIMB_1 << bitno)) ? 1 : 0;
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}
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EXPORT_SYMBOL_GPL(mpi_test_bit);
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/****************
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* Set bit N of A.
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*/
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void mpi_set_bit(MPI a, unsigned int n)
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{
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unsigned int i, limbno, bitno;
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limbno = n / BITS_PER_MPI_LIMB;
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bitno = n % BITS_PER_MPI_LIMB;
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if (limbno >= a->nlimbs) {
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for (i = a->nlimbs; i < a->alloced; i++)
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a->d[i] = 0;
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mpi_resize(a, limbno+1);
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a->nlimbs = limbno+1;
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}
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a->d[limbno] |= (A_LIMB_1<<bitno);
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}
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/****************
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* Set bit N of A. and clear all bits above
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*/
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void mpi_set_highbit(MPI a, unsigned int n)
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{
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unsigned int i, limbno, bitno;
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limbno = n / BITS_PER_MPI_LIMB;
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bitno = n % BITS_PER_MPI_LIMB;
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if (limbno >= a->nlimbs) {
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for (i = a->nlimbs; i < a->alloced; i++)
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a->d[i] = 0;
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mpi_resize(a, limbno+1);
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a->nlimbs = limbno+1;
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}
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a->d[limbno] |= (A_LIMB_1<<bitno);
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for (bitno++; bitno < BITS_PER_MPI_LIMB; bitno++)
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a->d[limbno] &= ~(A_LIMB_1 << bitno);
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a->nlimbs = limbno+1;
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}
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EXPORT_SYMBOL_GPL(mpi_set_highbit);
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/****************
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* clear bit N of A and all bits above
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*/
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void mpi_clear_highbit(MPI a, unsigned int n)
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{
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unsigned int limbno, bitno;
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limbno = n / BITS_PER_MPI_LIMB;
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bitno = n % BITS_PER_MPI_LIMB;
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if (limbno >= a->nlimbs)
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return; /* not allocated, therefore no need to clear bits :-) */
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for ( ; bitno < BITS_PER_MPI_LIMB; bitno++)
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a->d[limbno] &= ~(A_LIMB_1 << bitno);
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a->nlimbs = limbno+1;
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}
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/****************
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* Clear bit N of A.
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*/
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void mpi_clear_bit(MPI a, unsigned int n)
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{
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unsigned int limbno, bitno;
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limbno = n / BITS_PER_MPI_LIMB;
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bitno = n % BITS_PER_MPI_LIMB;
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if (limbno >= a->nlimbs)
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return; /* Don't need to clear this bit, it's far too left. */
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a->d[limbno] &= ~(A_LIMB_1 << bitno);
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}
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EXPORT_SYMBOL_GPL(mpi_clear_bit);
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/****************
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* Shift A by COUNT limbs to the right
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* This is used only within the MPI library
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*/
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void mpi_rshift_limbs(MPI a, unsigned int count)
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{
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mpi_ptr_t ap = a->d;
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mpi_size_t n = a->nlimbs;
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unsigned int i;
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if (count >= n) {
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a->nlimbs = 0;
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return;
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}
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for (i = 0; i < n - count; i++)
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ap[i] = ap[i+count];
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ap[i] = 0;
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a->nlimbs -= count;
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}
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/*
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* Shift A by N bits to the right.
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*/
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void mpi_rshift(MPI x, MPI a, unsigned int n)
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{
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mpi_size_t xsize;
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unsigned int i;
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unsigned int nlimbs = (n/BITS_PER_MPI_LIMB);
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unsigned int nbits = (n%BITS_PER_MPI_LIMB);
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if (x == a) {
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/* In-place operation. */
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if (nlimbs >= x->nlimbs) {
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x->nlimbs = 0;
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return;
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}
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if (nlimbs) {
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for (i = 0; i < x->nlimbs - nlimbs; i++)
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x->d[i] = x->d[i+nlimbs];
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x->d[i] = 0;
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x->nlimbs -= nlimbs;
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}
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if (x->nlimbs && nbits)
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mpihelp_rshift(x->d, x->d, x->nlimbs, nbits);
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} else if (nlimbs) {
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/* Copy and shift by more or equal bits than in a limb. */
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xsize = a->nlimbs;
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x->sign = a->sign;
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RESIZE_IF_NEEDED(x, xsize);
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x->nlimbs = xsize;
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for (i = 0; i < a->nlimbs; i++)
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x->d[i] = a->d[i];
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x->nlimbs = i;
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if (nlimbs >= x->nlimbs) {
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x->nlimbs = 0;
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return;
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}
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if (nlimbs) {
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for (i = 0; i < x->nlimbs - nlimbs; i++)
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x->d[i] = x->d[i+nlimbs];
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x->d[i] = 0;
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x->nlimbs -= nlimbs;
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}
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if (x->nlimbs && nbits)
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mpihelp_rshift(x->d, x->d, x->nlimbs, nbits);
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} else {
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/* Copy and shift by less than bits in a limb. */
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xsize = a->nlimbs;
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x->sign = a->sign;
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RESIZE_IF_NEEDED(x, xsize);
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x->nlimbs = xsize;
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if (xsize) {
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if (nbits)
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mpihelp_rshift(x->d, a->d, x->nlimbs, nbits);
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else {
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/* The rshift helper function is not specified for
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* NBITS==0, thus we do a plain copy here.
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*/
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for (i = 0; i < x->nlimbs; i++)
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x->d[i] = a->d[i];
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}
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}
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}
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MPN_NORMALIZE(x->d, x->nlimbs);
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}
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EXPORT_SYMBOL_GPL(mpi_rshift);
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/****************
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* Shift A by COUNT limbs to the left
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* This is used only within the MPI library
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*/
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void mpi_lshift_limbs(MPI a, unsigned int count)
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{
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mpi_ptr_t ap;
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int n = a->nlimbs;
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int i;
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if (!count || !n)
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return;
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RESIZE_IF_NEEDED(a, n+count);
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ap = a->d;
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for (i = n-1; i >= 0; i--)
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ap[i+count] = ap[i];
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for (i = 0; i < count; i++)
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ap[i] = 0;
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a->nlimbs += count;
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}
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/*
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* Shift A by N bits to the left.
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*/
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void mpi_lshift(MPI x, MPI a, unsigned int n)
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{
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unsigned int nlimbs = (n/BITS_PER_MPI_LIMB);
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unsigned int nbits = (n%BITS_PER_MPI_LIMB);
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if (x == a && !n)
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return; /* In-place shift with an amount of zero. */
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if (x != a) {
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/* Copy A to X. */
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unsigned int alimbs = a->nlimbs;
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int asign = a->sign;
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mpi_ptr_t xp, ap;
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RESIZE_IF_NEEDED(x, alimbs+nlimbs+1);
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xp = x->d;
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ap = a->d;
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MPN_COPY(xp, ap, alimbs);
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x->nlimbs = alimbs;
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x->flags = a->flags;
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x->sign = asign;
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}
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if (nlimbs && !nbits) {
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/* Shift a full number of limbs. */
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mpi_lshift_limbs(x, nlimbs);
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} else if (n) {
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/* We use a very dump approach: Shift left by the number of
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* limbs plus one and than fix it up by an rshift.
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*/
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mpi_lshift_limbs(x, nlimbs+1);
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mpi_rshift(x, x, BITS_PER_MPI_LIMB - nbits);
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}
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MPN_NORMALIZE(x->d, x->nlimbs);
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}
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