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