1/* mpihelp-add_1.c - MPI helper functions 2 * Copyright (C) 1994, 1996, 1997, 1998, 3 * 2000 Free Software Foundation, Inc. 4 * 5 * This file is part of GnuPG. 6 * 7 * GnuPG is free software; you can redistribute it and/or modify 8 * it under the terms of the GNU General Public License as published by 9 * the Free Software Foundation; either version 2 of the License, or 10 * (at your option) any later version. 11 * 12 * GnuPG is distributed in the hope that it will be useful, 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 15 * GNU General Public License for more details. 16 * 17 * You should have received a copy of the GNU General Public License 18 * along with this program; if not, write to the Free Software 19 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA 20 * 21 * Note: This code is heavily based on the GNU MP Library. 22 * Actually it's the same code with only minor changes in the 23 * way the data is stored; this is to support the abstraction 24 * of an optional secure memory allocation which may be used 25 * to avoid revealing of sensitive data due to paging etc. 26 * The GNU MP Library itself is published under the LGPL; 27 * however I decided to publish this code under the plain GPL. 28 */ 29 30#include "mpi-internal.h" 31#include "longlong.h" 32 33mpi_limb_t 34mpihelp_add_n(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr, 35 mpi_ptr_t s2_ptr, mpi_size_t size) 36{ 37 mpi_limb_t x, y, cy; 38 mpi_size_t j; 39 40 /* The loop counter and index J goes from -SIZE to -1. This way 41 the loop becomes faster. */ 42 j = -size; 43 44 /* Offset the base pointers to compensate for the negative indices. */ 45 s1_ptr -= j; 46 s2_ptr -= j; 47 res_ptr -= j; 48 49 cy = 0; 50 do { 51 y = s2_ptr[j]; 52 x = s1_ptr[j]; 53 y += cy; /* add previous carry to one addend */ 54 cy = y < cy; /* get out carry from that addition */ 55 y += x; /* add other addend */ 56 cy += y < x; /* get out carry from that add, combine */ 57 res_ptr[j] = y; 58 } while (++j); 59 60 return cy; 61} 62