/* mpi-add.c  -  MPI functions

 * Copyright (C) 1994, 1996, 1998, 2001, 2002, 2003 Free Software Foundation, Inc.

 *

 * This file is part of Libgcrypt.

 *

 * Libgcrypt is free software; you can redistribute it and/or modify

 * it under the terms of the GNU Lesser General Public License as

 * published by the Free Software Foundation; either version 2.1 of

 * the License, or (at your option) any later version.

 *

 * Libgcrypt 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 Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public

 * License along with this program; if not, see <https://www.gnu.org/licenses/>.

 * SPDX-License-Identifier: LGPL-2.1-or-later

 *

 * 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.

 */

#include <config.h>

#include <stdio.h>

#include <stdlib.h>

#include "mpi-internal.h"

/****************

 * Add the unsigned integer V to the mpi-integer U and store the

 * result in W. U and V may be the same.

 */

void

_gcry_mpi_add_ui (gcry_mpi_t w, gcry_mpi_t u, unsigned long v )

{

    mpi_ptr_t wp, up;

    mpi_size_t usize, wsize;

    int usign, wsign;

    usize = u->nlimbs;

    usign = u->sign;

    wsign = 0;

    /* If not space for W (and possible carry), increase space.  */

    wsize = usize + 1;

    if( w->alloced < wsize )

  mpi_resize(w, wsize);

    /* These must be after realloc (U may be the same as W).  */

    up = u->d;

    wp = w->d;

    if( !usize ) {  /* simple */

  wp[0] = v;

  wsize = v? 1:0;

    }

    else if( !usign ) {  /* mpi is not negative */

  mpi_limb_t cy;

  cy = _gcry_mpih_add_1(wp, up, usize, v);

  wp[usize] = cy;

  wsize = usize + cy;

    }

    else {  /* The signs are different.  Need exact comparison to determine

       * which operand to subtract from which.  */

  if( usize == 1 && up[0] < v ) {

      wp[0] = v - up[0];

      wsize = 1;

  }

  else {

      _gcry_mpih_sub_1(wp, up, usize, v);

      /* Size can decrease with at most one limb. */

      wsize = usize - (wp[usize-1]==0);

      wsign = 1;

  }

    }

    w->nlimbs = wsize;

    w->sign   = wsign;

}

static void

_gcry_mpi_add_inv_sign(gcry_mpi_t w, gcry_mpi_t u, gcry_mpi_t v, int inv_v_sign)

{

    mpi_ptr_t wp, up, vp;

    mpi_size_t usize, vsize, wsize;

    int usign, vsign, wsign;

    if( u->nlimbs < v->nlimbs ) { /* Swap U and V. */

  usize = v->nlimbs;

  usign = v->sign ^ inv_v_sign;

  vsize = u->nlimbs;

  vsign = u->sign;

  wsize = usize + 1;

  RESIZE_IF_NEEDED(w, wsize);

  /* These must be after realloc (u or v may be the same as w).  */

  up    = v->d;

  vp    = u->d;

    }

    else {

  usize = u->nlimbs;

  usign = u->sign;

  vsize = v->nlimbs;

  vsign = v->sign ^ inv_v_sign;

  wsize = usize + 1;

  RESIZE_IF_NEEDED(w, wsize);

  /* These must be after realloc (u or v may be the same as w).  */

  up    = u->d;

  vp    = v->d;

    }

    wp = w->d;

    wsign = 0;

    if( !vsize ) {  /* simple */

  MPN_COPY(wp, up, usize );

  wsize = usize;

  wsign = usign;

    }

    else if( usign != vsign ) { /* different sign */

  /* This test is right since USIZE >= VSIZE */

  if( usize != vsize ) {

      _gcry_mpih_sub(wp, up, usize, vp, vsize);

      wsize = usize;

      MPN_NORMALIZE(wp, wsize);

      wsign = usign;

  }

  else if( _gcry_mpih_cmp(up, vp, usize) < 0 ) {

      _gcry_mpih_sub_n(wp, vp, up, usize);

      wsize = usize;

      MPN_NORMALIZE(wp, wsize);

      if( !usign )

    wsign = 1;

  }

  else {

      _gcry_mpih_sub_n(wp, up, vp, usize);

      wsize = usize;

      MPN_NORMALIZE(wp, wsize);

      if( usign )

    wsign = 1;

  }

    }

    else { /* U and V have same sign. Add them. */

  mpi_limb_t cy = _gcry_mpih_add(wp, up, usize, vp, vsize);

  wp[usize] = cy;

  wsize = usize + cy;

  if( usign )

      wsign = 1;

    }

    w->nlimbs = wsize;

    w->sign = wsign;

}

/****************

 * Subtract the unsigned integer V from the mpi-integer U and store the

 * result in W.

 */

void

_gcry_mpi_sub_ui(gcry_mpi_t w, gcry_mpi_t u, unsigned long v )

{

    mpi_ptr_t wp, up;

    mpi_size_t usize, wsize;

    int usign, wsign;

    usize = u->nlimbs;

    usign = u->sign;

    wsign = 0;

    /* If not space for W (and possible carry), increase space.  */

    wsize = usize + 1;

    if( w->alloced < wsize )

  mpi_resize(w, wsize);

    /* These must be after realloc (U may be the same as W).  */

    up = u->d;

    wp = w->d;

    if( !usize ) {  /* simple */

  wp[0] = v;

  wsize = v? 1:0;

  wsign = 1;

    }

    else if( usign ) { /* mpi and v are negative */

  mpi_limb_t cy;

  cy = _gcry_mpih_add_1(wp, up, usize, v);

  wp[usize] = cy;

  wsize = usize + cy;

  wsign = 1;

    }

    else {  /* The signs are different.  Need exact comparison to determine

       * which operand to subtract from which.  */

  if( usize == 1 && up[0] < v ) {

      wp[0] = v - up[0];

      wsize = 1;

      wsign = 1;

  }

  else {

      _gcry_mpih_sub_1(wp, up, usize, v);

      /* Size can decrease with at most one limb. */

      wsize = usize - (wp[usize-1]==0);

  }

    }

    w->nlimbs = wsize;

    w->sign   = wsign;

}

void

_gcry_mpi_add(gcry_mpi_t w, gcry_mpi_t u, gcry_mpi_t v)

{

  _gcry_mpi_add_inv_sign (w, u, v, 0);

}

void

_gcry_mpi_sub(gcry_mpi_t w, gcry_mpi_t u, gcry_mpi_t v)

{

  _gcry_mpi_add_inv_sign (w, u, v, 1);

}

void

_gcry_mpi_addm( gcry_mpi_t w, gcry_mpi_t u, gcry_mpi_t v, gcry_mpi_t m)

{

  gcry_mpi_t temp_m = NULL;

  if (w == m)

    {

      temp_m = mpi_copy (m);

      m = temp_m;

    }

  mpi_add (w, u, v);

  mpi_mod (w, w, m);

  if (temp_m)

    mpi_free(temp_m);

}

void

_gcry_mpi_subm( gcry_mpi_t w, gcry_mpi_t u, gcry_mpi_t v, gcry_mpi_t m)

{

  gcry_mpi_t temp_m = NULL;

  if (w == m)

    {

      temp_m = mpi_copy (m);

      m = temp_m;

    }

  mpi_sub (w, u, v);

  mpi_mod (w, w, m);

  if (temp_m)

    mpi_free(temp_m);

}