mirror of git://git.gnupg.org/gnupg.git
115 lines
2.6 KiB
C
115 lines
2.6 KiB
C
/* mpi-scan.c - MPI functions
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* Copyright (c) 1997 by Werner Koch (dd9jn)
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*
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* This file is part of G10.
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*
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* G10 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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* G10 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 <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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/****************
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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
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mpi_getbyte( MPI a, unsigned index )
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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 == index )
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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 INDEX into A. index counts from lsb to msb
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*/
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void
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mpi_putbyte( MPI a, unsigned index, int c )
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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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#if BYTES_PER_MPI_LIMB != 4
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#error please enhance this function, its ugly - i know.
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#endif
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c &= 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 == index ) {
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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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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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abort(); /* index out of range */
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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
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mpi_trailing_zeros( 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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