Line data    Source code

       1             : /* mpi-scan.c  -  MPI functions
       2             :  *      Copyright (C) 1998, 2001, 2002, 2003 Free Software Foundation, Inc.
       3             :  *
       4             :  * This file is part of Libgcrypt.
       5             :  *
       6             :  * Libgcrypt is free software; you can redistribute it and/or modify
       7             :  * it under the terms of the GNU Lesser General Public License as
       8             :  * published by the Free Software Foundation; either version 2.1 of
       9             :  * the License, or (at your option) any later version.
      10             :  *
      11             :  * Libgcrypt is distributed in the hope that it will be useful,
      12             :  * but WITHOUT ANY WARRANTY; without even the implied warranty of
      13             :  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      14             :  * GNU Lesser General Public License for more details.
      15             :  *
      16             :  * You should have received a copy of the GNU Lesser General Public
      17             :  * License along with this program; if not, write to the Free Software
      18             :  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
      19             :  */
      20             : 
      21             : #include <config.h>
      22             : #include <stdio.h>
      23             : #include <stdlib.h>
      24             : #include "mpi-internal.h"
      25             : #include "longlong.h"
      26             : 
      27             : /****************
      28             :  * Scan through an mpi and return byte for byte. a -1 is returned to indicate
      29             :  * the end of the mpi. Scanning is done from the lsb to the msb, returned
      30             :  * values are in the range of 0 .. 255.
      31             :  *
      32             :  * FIXME: This code is VERY ugly!
      33             :  */
      34             : /* int */
      35             : /* _gcry_mpi_getbyte( gcry_mpi_t a, unsigned idx ) */
      36             : /* { */
      37             : /*     int i, j; */
      38             : /*     unsigned n; */
      39             : /*     mpi_ptr_t ap; */
      40             : /*     mpi_limb_t limb; */
      41             : 
      42             : /*     ap = a->d; */
      43             : /*     for(n=0,i=0; i < a->nlimbs; i++ ) { */
      44             : /*      limb = ap[i]; */
      45             : /*      for( j=0; j < BYTES_PER_MPI_LIMB; j++, n++ ) */
      46             : /*          if( n == idx ) */
      47             : /*              return (limb >> j*8) & 0xff; */
      48             : /*     } */
      49             : /*     return -1; */
      50             : /* } */
      51             : 
      52             : 
      53             : /****************
      54             :  * Put a value at position IDX into A. idx counts from lsb to msb
      55             :  */
      56             : /* void */
      57             : /* _gcry_mpi_putbyte( gcry_mpi_t a, unsigned idx, int xc ) */
      58             : /* { */
      59             : /*     int i, j; */
      60             : /*     unsigned n; */
      61             : /*     mpi_ptr_t ap; */
      62             : /*     mpi_limb_t limb, c; */
      63             : 
      64             : /*     c = xc & 0xff; */
      65             : /*     ap = a->d; */
      66             : /*     for(n=0,i=0; i < a->alloced; i++ ) { */
      67             : /*      limb = ap[i]; */
      68             : /*      for( j=0; j < BYTES_PER_MPI_LIMB; j++, n++ ) */
      69             : /*          if( n == idx ) { */
      70             : /*            #if BYTES_PER_MPI_LIMB == 4 */
      71             : /*              if( j == 0 ) */
      72             : /*                  limb = (limb & 0xffffff00) | c; */
      73             : /*              else if( j == 1 ) */
      74             : /*                  limb = (limb & 0xffff00ff) | (c<<8); */
      75             : /*              else if( j == 2 ) */
      76             : /*                  limb = (limb & 0xff00ffff) | (c<<16); */
      77             : /*              else */
      78             : /*                  limb = (limb & 0x00ffffff) | (c<<24); */
      79             : /*            #elif BYTES_PER_MPI_LIMB == 8 */
      80             : /*              if( j == 0 ) */
      81             : /*                  limb = (limb & 0xffffffffffffff00) | c; */
      82             : /*              else if( j == 1 ) */
      83             : /*                  limb = (limb & 0xffffffffffff00ff) | (c<<8); */
      84             : /*              else if( j == 2 ) */
      85             : /*                  limb = (limb & 0xffffffffff00ffff) | (c<<16); */
      86             : /*              else if( j == 3 ) */
      87             : /*                  limb = (limb & 0xffffffff00ffffff) | (c<<24); */
      88             : /*              else if( j == 4 ) */
      89             : /*                  limb = (limb & 0xffffff00ffffffff) | (c<<32); */
      90             : /*              else if( j == 5 ) */
      91             : /*                  limb = (limb & 0xffff00ffffffffff) | (c<<40); */
      92             : /*              else if( j == 6 ) */
      93             : /*                  limb = (limb & 0xff00ffffffffffff) | (c<<48); */
      94             : /*              else */
      95             : /*                  limb = (limb & 0x00ffffffffffffff) | (c<<56); */
      96             : /*            #else */
      97             : /*               #error please enhance this function, its ugly - i know. */
      98             : /*            #endif */
      99             : /*              if( a->nlimbs <= i ) */
     100             : /*                  a->nlimbs = i+1; */
     101             : /*              ap[i] = limb; */
     102             : /*              return; */
     103             : /*          } */
     104             : /*     } */
     105             : /*     abort(); /\* index out of range *\/ */
     106             : /* } */
     107             : 
     108             : 
     109             : /****************
     110             :  * Count the number of zerobits at the low end of A
     111             :  */
     112             : unsigned
     113         590 : _gcry_mpi_trailing_zeros( gcry_mpi_t a )
     114             : {
     115         590 :     unsigned n, count = 0;
     116             : 
     117         590 :     for(n=0; n < a->nlimbs; n++ ) {
     118         590 :         if( a->d[n] ) {
     119             :             unsigned nn;
     120         590 :             mpi_limb_t alimb = a->d[n];
     121             : 
     122         590 :             count_trailing_zeros( nn, alimb );
     123         590 :             count += nn;
     124         590 :             break;
     125             :         }
     126           0 :         count += BITS_PER_MPI_LIMB;
     127             :     }
     128         590 :     return count;
     129             : 
     130             : }