1/* mpih-mul3.c - MPI helper functions 2 * Copyright (C) 1994, 1996, 1997, 1998, 2001, 3 * 2002 Free Software Foundation, Inc. 4 * 5 * This file is part of Libgcrypt. 6 * 7 * Libgcrypt is free software; you can redistribute it and/or modify 8 * it under the terms of the GNU Lesser General Public License as 9 * published by the Free Software Foundation; either version 2.1 of 10 * the License, or (at your option) any later version. 11 * 12 * Libgcrypt 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 Lesser General Public License for more details. 16 * 17 * You should have received a copy of the GNU Lesser General Public 18 * License 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 */ 27 28#include <config.h> 29#include <stdio.h> 30#include <stdlib.h> 31#include "mpi-internal.h" 32#include "longlong.h" 33 34 35mpi_limb_t 36_gcry_mpih_submul_1( mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr, 37 mpi_size_t s1_size, mpi_limb_t s2_limb) 38{ 39 mpi_limb_t cy_limb; 40 mpi_size_t j; 41 mpi_limb_t prod_high, prod_low; 42 mpi_limb_t x; 43 44 /* The loop counter and index J goes from -SIZE to -1. This way 45 * the loop becomes faster. */ 46 j = -s1_size; 47 res_ptr -= j; 48 s1_ptr -= j; 49 50 cy_limb = 0; 51 do 52 { 53 umul_ppmm( prod_high, prod_low, s1_ptr[j], s2_limb); 54 55 prod_low += cy_limb; 56 cy_limb = (prod_low < cy_limb?1:0) + prod_high; 57 58 x = res_ptr[j]; 59 prod_low = x - prod_low; 60 cy_limb += prod_low > x?1:0; 61 res_ptr[j] = prod_low; 62 } 63 while( ++j ); 64 65 return cy_limb; 66} 67 68 69