^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 1) // SPDX-License-Identifier: GPL-2.0-or-later
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 2) /* mpihelp-add_1.c - MPI helper functions
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 3) * Copyright (C) 1994, 1996, 1997, 1998,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 4) * 2000 Free Software Foundation, Inc.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 5) *
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 6) * This file is part of GnuPG.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 7) *
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 8) * Note: This code is heavily based on the GNU MP Library.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 9) * Actually it's the same code with only minor changes in the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10) * way the data is stored; this is to support the abstraction
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11) * of an optional secure memory allocation which may be used
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12) * to avoid revealing of sensitive data due to paging etc.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13) * The GNU MP Library itself is published under the LGPL;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14) * however I decided to publish this code under the plain GPL.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15) */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17) #include "mpi-internal.h"
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18) #include "longlong.h"
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20) mpi_limb_t
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21) mpihelp_add_n(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22) mpi_ptr_t s2_ptr, mpi_size_t size)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24) mpi_limb_t x, y, cy;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) mpi_size_t j;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27) /* The loop counter and index J goes from -SIZE to -1. This way
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) the loop becomes faster. */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29) j = -size;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31) /* Offset the base pointers to compensate for the negative indices. */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32) s1_ptr -= j;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33) s2_ptr -= j;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34) res_ptr -= j;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36) cy = 0;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37) do {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38) y = s2_ptr[j];
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39) x = s1_ptr[j];
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40) y += cy; /* add previous carry to one addend */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41) cy = y < cy; /* get out carry from that addition */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42) y += x; /* add other addend */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 43) cy += y < x; /* get out carry from that add, combine */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 44) res_ptr[j] = y;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 45) } while (++j);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 46)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 47) return cy;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 48) }