LXR linux/lib/mpi/generic

   1// SPDX-License-Identifier: GPL-2.0-or-later
   2/* mpihelp-add_1.c  -  MPI helper functions
   3 * Copyright (C) 1994, 1996, 1997, 1998,
   4 *               2000 Free Software Foundation, Inc.
   5 *
   6 * This file is part of GnuPG.
   7 *
   8 * Note: This code is heavily based on the GNU MP Library.
   9 *       Actually it's the same code with only minor changes in the
  10 *       way the data is stored; this is to support the abstraction
  11 *       of an optional secure memory allocation which may be used
  12 *       to avoid revealing of sensitive data due to paging etc.
  13 *       The GNU MP Library itself is published under the LGPL;
  14 *       however I decided to publish this code under the plain GPL.
  15 */
  16
  17#include "mpi-internal.h"
  18#include "longlong.h"
  19
  20mpi_limb_t
  21mpihelp_add_n(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
  22              mpi_ptr_t s2_ptr, mpi_size_t size)
  23{
  24        mpi_limb_t x, y, cy;
  25        mpi_size_t j;
  26
  27        /* The loop counter and index J goes from -SIZE to -1.  This way
  28           the loop becomes faster.  */
  29        j = -size;
  30
  31        /* Offset the base pointers to compensate for the negative indices. */
  32        s1_ptr -= j;
  33        s2_ptr -= j;
  34        res_ptr -= j;
  35
  36        cy = 0;
  37        do {
  38                y = s2_ptr[j];
  39                x = s1_ptr[j];
  40                y += cy;        /* add previous carry to one addend */
  41                cy = y < cy;    /* get out carry from that addition */
  42                y += x;         /* add other addend */
  43                cy += y < x;    /* get out carry from that add, combine */
  44                res_ptr[j] = y;
  45        } while (++j);
  46
  47        return cy;
  48}
  49