github.com/aergoio/aergo@v1.3.1/libtool/src/gmp-6.1.2/mpn/generic/sec_tabselect.c (about)

     1  /* mpn_sec_tabselect.
     2  
     3  Copyright 2007-2009, 2011, 2013 Free Software Foundation, Inc.
     4  
     5  This file is part of the GNU MP Library.
     6  
     7  The GNU MP Library is free software; you can redistribute it and/or modify
     8  it under the terms of either:
     9  
    10    * the GNU Lesser General Public License as published by the Free
    11      Software Foundation; either version 3 of the License, or (at your
    12      option) any later version.
    13  
    14  or
    15  
    16    * the GNU General Public License as published by the Free Software
    17      Foundation; either version 2 of the License, or (at your option) any
    18      later version.
    19  
    20  or both in parallel, as here.
    21  
    22  The GNU MP Library is distributed in the hope that it will be useful, but
    23  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
    24  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
    25  for more details.
    26  
    27  You should have received copies of the GNU General Public License and the
    28  GNU Lesser General Public License along with the GNU MP Library.  If not,
    29  see https://www.gnu.org/licenses/.  */
    30  
    31  #include "gmp.h"
    32  #include "gmp-impl.h"
    33  
    34  
    35  /* Select entry `which' from table `tab', which has nents entries, each `n'
    36     limbs.  Store the selected entry at rp.  Reads entire table to avoid
    37     side-channel information leaks.  O(n*nents).  */
    38  void
    39  mpn_sec_tabselect (volatile mp_limb_t *rp, volatile const mp_limb_t *tab,
    40  		   mp_size_t n, mp_size_t nents, mp_size_t which)
    41  {
    42    mp_size_t k, i;
    43    mp_limb_t mask;
    44    volatile const mp_limb_t *tp;
    45  
    46    for (k = 0; k < nents; k++)
    47      {
    48        mask = -(mp_limb_t) (which == k);
    49        tp = tab + n * k;
    50        for (i = 0; i < n; i++)
    51  	{
    52  	  rp[i] = (rp[i] & ~mask) | (tp[i] & mask);
    53  	}
    54      }
    55  }