61 lines
2.0 KiB
C
61 lines
2.0 KiB
C
|
/* mpihelp-add_2.c - MPI helper functions
|
||
|
|
* Copyright (C) 1994, 1996, 1997, 1998, 2001 Free Software Foundation, Inc.
|
||
|
|
*
|
||
|
|
* This file is part of GnuPG.
|
||
|
|
*
|
||
|
|
* GnuPG is free software; you can redistribute it and/or modify
|
||
|
|
* it under the terms of the GNU General Public License as published by
|
||
|
|
* the Free Software Foundation; either version 2 of the License, or
|
||
|
|
* (at your option) any later version.
|
||
|
|
*
|
||
|
|
* GnuPG is distributed in the hope that it will be useful,
|
||
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
||
|
|
* GNU General Public License for more details.
|
||
|
|
*
|
||
|
|
* You should have received a copy of the GNU General Public License
|
||
|
|
* along with this program; if not, write to the Free Software
|
||
|
|
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
|
||
|
|
*
|
||
|
|
* Note: This code is heavily based on the GNU MP Library.
|
||
|
|
* Actually it's the same code with only minor changes in the
|
||
|
|
* way the data is stored; this is to support the abstraction
|
||
|
|
* of an optional secure memory allocation which may be used
|
||
|
|
* to avoid revealing of sensitive data due to paging etc.
|
||
|
|
* The GNU MP Library itself is published under the LGPL;
|
||
|
|
* however I decided to publish this code under the plain GPL.
|
||
|
|
*/
|
||
|
|
|
||
|
|
#include "mpi-internal.h"
|
||
|
|
#include "longlong.h"
|
||
|
|
|
||
|
|
mpi_limb_t
|
||
|
|
mpihelp_sub_n(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
|
||
|
|
mpi_ptr_t s2_ptr, mpi_size_t size)
|
||
|
|
{
|
||
|
|
mpi_limb_t x, y, cy;
|
||
|
|
mpi_size_t j;
|
||
|
|
|
||
|
|
/* The loop counter and index J goes from -SIZE to -1. This way
|
||
|
|
the loop becomes faster. */
|
||
|
|
j = -size;
|
||
|
|
|
||
|
|
/* Offset the base pointers to compensate for the negative indices. */
|
||
|
|
s1_ptr -= j;
|
||
|
|
s2_ptr -= j;
|
||
|
|
res_ptr -= j;
|
||
|
|
|
||
|
|
cy = 0;
|
||
|
|
do {
|
||
|
|
y = s2_ptr[j];
|
||
|
|
x = s1_ptr[j];
|
||
|
|
y += cy; /* add previous carry to subtrahend */
|
||
|
|
cy = y < cy; /* get out carry from that addition */
|
||
|
|
y = x - y; /* main subtract */
|
||
|
|
cy += y > x; /* get out carry from the subtract, combine */
|
||
|
|
res_ptr[j] = y;
|
||
|
|
} while (++j);
|
||
|
|
|
||
|
|
return cy;
|
||
|
|
}
|