lib/mpi/generic_mpih-mul1.c

   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 }