linux/lib/mpi/generic_mpih-mul1.c
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   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