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generic_mpih-add1.c

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    • Dmitry Kasatkin's avatar
      cdec9cb5
      crypto: GnuPG based MPI lib - source files (part 1) · cdec9cb5
      Dmitry Kasatkin authored
      
      Adds the multi-precision-integer maths library which was originally taken
      from GnuPG and ported to the kernel by (among others) David Howells.
      This version is taken from Fedora kernel 2.6.32-71.14.1.el6.
      The difference is that checkpatch reported errors and warnings have been fixed.
      
      This library is used to implemenet RSA digital signature verification
      used in IMA/EVM integrity protection subsystem.
      
      Due to patch size limitation, the patch is divided into 4 parts.
      
      Signed-off-by: default avatarDmitry Kasatkin <dmitry.kasatkin@intel.com>
      cdec9cb5
      History
      crypto: GnuPG based MPI lib - source files (part 1)
      Dmitry Kasatkin authored
      
      Adds the multi-precision-integer maths library which was originally taken
      from GnuPG and ported to the kernel by (among others) David Howells.
      This version is taken from Fedora kernel 2.6.32-71.14.1.el6.
      The difference is that checkpatch reported errors and warnings have been fixed.
      
      This library is used to implemenet RSA digital signature verification
      used in IMA/EVM integrity protection subsystem.
      
      Due to patch size limitation, the patch is divided into 4 parts.
      
      Signed-off-by: default avatarDmitry Kasatkin <dmitry.kasatkin@intel.com>
    generic_mpih-add1.c 1.98 KiB
    /* mpihelp-add_1.c  -  MPI helper functions
     * Copyright (C) 1994, 1996, 1997, 1998,
     *               2000 Free Software Foundation, Inc.
     *
     * This file is part of GnuPG.
     *
     * GnuPG is free software; you can redistribute it and/or modify
     * it under the terms of the GNU General Public License as published by
     * the Free Software Foundation; either version 2 of the License, or
     * (at your option) any later version.
     *
     * GnuPG is distributed in the hope that it will be useful,
     * but WITHOUT ANY WARRANTY; without even the implied warranty of
     * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     * GNU General Public License for more details.
     *
     * You should have received a copy of the GNU General Public License
     * along with this program; if not, write to the Free Software
     * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
     *
     * Note: This code is heavily based on the GNU MP Library.
     *	 Actually it's the same code with only minor changes in the
     *	 way the data is stored; this is to support the abstraction
     *	 of an optional secure memory allocation which may be used
     *	 to avoid revealing of sensitive data due to paging etc.
     *	 The GNU MP Library itself is published under the LGPL;
     *	 however I decided to publish this code under the plain GPL.
     */
    
    #include "mpi-internal.h"
    #include "longlong.h"
    
    mpi_limb_t
    mpihelp_add_n(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
    	      mpi_ptr_t s2_ptr, mpi_size_t size)
    {
    	mpi_limb_t x, y, cy;
    	mpi_size_t j;
    
    	/* The loop counter and index J goes from -SIZE to -1.  This way
    	   the loop becomes faster.  */
    	j = -size;
    
    	/* Offset the base pointers to compensate for the negative indices. */
    	s1_ptr -= j;
    	s2_ptr -= j;
    	res_ptr -= j;
    
    	cy = 0;
    	do {
    		y = s2_ptr[j];
    		x = s1_ptr[j];
    		y += cy;	/* add previous carry to one addend */
    		cy = y < cy;	/* get out carry from that addition */
    		y += x;		/* add other addend */
    		cy += y < x;	/* get out carry from that add, combine */
    		res_ptr[j] = y;
    	} while (++j);
    
    	return cy;
    }