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365 lines
8.1 KiB
C
365 lines
8.1 KiB
C
/* mpi-bit.c - MPI bit level functions
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* Copyright (C) 1998, 1999, 2001, 2002, 2006 Free Software Foundation, Inc.
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*
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* This file is part of Libgcrypt.
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*
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* Libgcrypt is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as
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* published by the Free Software Foundation; either version 2.1 of
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* the License, or (at your option) any later version.
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*
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* Libgcrypt 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 Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License 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 <config.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include "mpi-internal.h"
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#include "longlong.h"
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#ifdef MPI_INTERNAL_NEED_CLZ_TAB
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#ifdef __STDC__
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const
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#endif
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unsigned char
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_gcry_clz_tab[] =
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{
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0,1,2,2,3,3,3,3,4,4,4,4,4,4,4,4,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
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6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
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7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
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7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
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8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
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8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
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8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
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8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
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};
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#endif
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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
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_gcry_mpi_normalize( gcry_mpi_t a )
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{
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if( mpi_is_opaque(a) )
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return;
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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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/****************
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* Return the number of bits in A.
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*/
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unsigned int
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gcry_mpi_get_nbits( gcry_mpi_t a )
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{
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unsigned n;
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if( mpi_is_opaque(a) ) {
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return a->sign; /* which holds the number of bits */
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}
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_gcry_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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count_leading_zeros( n, 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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}
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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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/****************
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* Test whether bit N is set.
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*/
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int
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gcry_mpi_test_bit( gcry_mpi_t 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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/****************
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* Set bit N of A.
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*/
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void
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gcry_mpi_set_bit( gcry_mpi_t 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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{
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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
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gcry_mpi_set_highbit( gcry_mpi_t 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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{
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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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/****************
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* clear bit N of A and all bits above
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*/
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void
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gcry_mpi_clear_highbit( gcry_mpi_t 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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:-) */
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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
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gcry_mpi_clear_bit( gcry_mpi_t 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 to far to left */
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a->d[limbno] &= ~(A_LIMB_1 << bitno);
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}
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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
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_gcry_mpi_rshift_limbs( gcry_mpi_t 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
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gcry_mpi_rshift ( gcry_mpi_t x, gcry_mpi_t 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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{
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/* In-place operation. */
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if ( nlimbs >= x->nlimbs )
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{
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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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{
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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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_gcry_mpih_rshift ( x->d, x->d, x->nlimbs, nbits );
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}
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else if ( nlimbs )
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{
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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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{
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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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{
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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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_gcry_mpih_rshift ( x->d, x->d, x->nlimbs, nbits );
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}
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else
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{
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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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{
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if (nbits )
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_gcry_mpih_rshift (x->d, a->d, x->nlimbs, nbits );
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else
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{
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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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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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/****************
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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
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_gcry_mpi_lshift_limbs (gcry_mpi_t 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
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gcry_mpi_lshift ( gcry_mpi_t x, gcry_mpi_t 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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{
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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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{
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/* Shift a full number of limbs. */
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_gcry_mpi_lshift_limbs (x, nlimbs);
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}
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else if (n)
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{
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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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_gcry_mpi_lshift_limbs (x, nlimbs+1);
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gcry_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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