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- // 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;
- }
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