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
19mpi_limb_t
20mpihelp_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