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1// SPDX-License-Identifier: GPL-2.0-or-later2/* mpihelp-add_1.c - MPI helper functions3 * 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 the10 * way the data is stored; this is to support the abstraction11 * of an optional secure memory allocation which may be used12 * 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_t21mpihelp_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 way28 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