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 20 mpi_limb_t 21 mpihelp_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