lib/mpi/generic_mpih-mul1.c

0001 // SPDX-License-Identifier: GPL-2.0-or-later
0002 /* mpihelp-mul_1.c  -  MPI helper functions
0003  * Copyright (C) 1994, 1996, 1997, 1998, 2001 Free Software Foundation, Inc.
0004  *
0005  * This file is part of GnuPG.
0006  *
0007  * Note: This code is heavily based on the GNU MP Library.
0008  *   Actually it's the same code with only minor changes in the
0009  *   way the data is stored; this is to support the abstraction
0010  *   of an optional secure memory allocation which may be used
0011  *   to avoid revealing of sensitive data due to paging etc.
0012  *   The GNU MP Library itself is published under the LGPL;
0013  *   however I decided to publish this code under the plain GPL.
0014  */
0015
0016 #include "mpi-internal.h"
0017 #include "longlong.h"
0018
0019 mpi_limb_t
0020 mpihelp_mul_1(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr, mpi_size_t s1_size,
0021           mpi_limb_t s2_limb)
0022 {
0023     mpi_limb_t cy_limb;
0024     mpi_size_t j;
0025     mpi_limb_t prod_high, prod_low;
0026
0027     /* The loop counter and index J goes from -S1_SIZE to -1.  This way
0028      * the loop becomes faster.  */
0029     j = -s1_size;
0030
0031     /* Offset the base pointers to compensate for the negative indices.  */
0032     s1_ptr -= j;
0033     res_ptr -= j;
0034
0035     cy_limb = 0;
0036     do {
0037         umul_ppmm(prod_high, prod_low, s1_ptr[j], s2_limb);
0038         prod_low += cy_limb;
0039         cy_limb = (prod_low < cy_limb ? 1 : 0) + prod_high;
0040         res_ptr[j] = prod_low;
0041     } while (++j);
0042
0043     return cy_limb;
0044 }