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       1                 :            : // SPDX-License-Identifier: GPL-2.0-or-later
       2                 :            : /* mpihelp-mul_3.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                 :       5984 : mpihelp_submul_1(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
      21                 :            :                  mpi_size_t s1_size, mpi_limb_t s2_limb)
      22                 :            : {
      23                 :       5984 :         mpi_limb_t cy_limb;
      24                 :       5984 :         mpi_size_t j;
      25                 :       5984 :         mpi_limb_t prod_high, prod_low;
      26                 :       5984 :         mpi_limb_t x;
      27                 :            : 
      28                 :            :         /* The loop counter and index J goes from -SIZE to -1.  This way
      29                 :            :          * the loop becomes faster.  */
      30                 :       5984 :         j = -s1_size;
      31                 :       5984 :         res_ptr -= j;
      32                 :       5984 :         s1_ptr -= j;
      33                 :            : 
      34                 :       5984 :         cy_limb = 0;
      35                 :     191488 :         do {
      36         [ +  + ]:     191488 :                 umul_ppmm(prod_high, prod_low, s1_ptr[j], s2_limb);
      37                 :            : 
      38                 :     191488 :                 prod_low += cy_limb;
      39         [ +  + ]:     191488 :                 cy_limb = (prod_low < cy_limb ? 1 : 0) + prod_high;
      40                 :            : 
      41                 :     191488 :                 x = res_ptr[j];
      42                 :     191488 :                 prod_low = x - prod_low;
      43         [ +  + ]:     191488 :                 cy_limb += prod_low > x ? 1 : 0;
      44                 :     191488 :                 res_ptr[j] = prod_low;
      45         [ +  + ]:     191488 :         } while (++j);
      46                 :            : 
      47                 :       5984 :         return cy_limb;
      48                 :            : }