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465ae836 | 1 | // SPDX-License-Identifier: GPL-2.0-or-later |
cdec9cb5 DK |
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 | * | |
cdec9cb5 DK |
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 | } |