1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* mpihelp-mul_1.c - MPI helper functions 3 * Copyright (C) 1994, 1996, 1997, 1998, 2001 Free Software Foundation, Inc. 4 * 5 * This file is part of GnuPG. 6 * 7 * Note: This code is heavily based on the GNU MP Library. 8 * Actually it's the same code with only minor changes in the 9 * way the data is stored; this is to support the abstraction 10 * of an optional secure memory allocation which may be used 11 * to avoid revealing of sensitive data due to paging etc. 12 * The GNU MP Library itself is published under the LGPL; 13 * however I decided to publish this code under the plain GPL. 14 */ 15 16 #include "mpi-internal.h" 17 #include "longlong.h" 18 19 mpi_limb_t 20 mpihelp_mul_1(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr, mpi_size_t s1_size, 21 mpi_limb_t s2_limb) 22 { 23 mpi_limb_t cy_limb; 24 mpi_size_t j; 25 mpi_limb_t prod_high, prod_low; 26 27 /* The loop counter and index J goes from -S1_SIZE to -1. This way 28 * the loop becomes faster. */ 29 j = -s1_size; 30 31 /* Offset the base pointers to compensate for the negative indices. */ 32 s1_ptr -= j; 33 res_ptr -= j; 34 35 cy_limb = 0; 36 do { 37 umul_ppmm(prod_high, prod_low, s1_ptr[j], s2_limb); 38 prod_low += cy_limb; 39 cy_limb = (prod_low < cy_limb ? 1 : 0) + prod_high; 40 res_ptr[j] = prod_low; 41 } while (++j); 42 43 return cy_limb; 44 } 45