// SPDX-License-Identifier: GPL-2.0-or-later
/* mpihelp-add_1.c  -  MPI helper functions
 * Copyright (C) 1994, 1996, 1997, 1998,
 *               2000 Free Software Foundation, Inc.
 *
 * This file is part of GnuPG.
 *
 * 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;
}