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 | |