view libtommath/bn_mp_tc_xor.c @ 1663:c795520269f9

Fallback for key gen without hard link support (#89) Add a non-atomic fallback for key generation on platforms where link() is not permitted (such as most stock Android installs) or on filesystems without hard link support (such as FAT).
author Matt Robinson <git@nerdoftheherd.com>
date Sat, 14 Mar 2020 14:37:35 +0000
parents f52919ffd3b1
children
line wrap: on
line source

#include "tommath_private.h"
#ifdef BN_MP_TC_XOR_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis
 *
 * LibTomMath is a library that provides multiple-precision
 * integer arithmetic as well as number theoretic functionality.
 *
 * The library was designed directly after the MPI library by
 * Michael Fromberger but has been written from scratch with
 * additional optimizations in place.
 *
 * SPDX-License-Identifier: Unlicense
 */

/* two complement xor */
int mp_tc_xor(const mp_int *a, const mp_int *b, mp_int *c)
{
   int res = MP_OKAY, bits, abits, bbits;
   int as = mp_isneg(a), bs = mp_isneg(b);
   mp_int *mx = NULL, _mx, acpy, bcpy;

   if ((as != MP_NO) || (bs != MP_NO)) {
      abits = mp_count_bits(a);
      bbits = mp_count_bits(b);
      bits = MAX(abits, bbits);
      res = mp_init_set_int(&_mx, 1uL);
      if (res != MP_OKAY) {
         goto end;
      }

      mx = &_mx;
      res = mp_mul_2d(mx, bits + 1, mx);
      if (res != MP_OKAY) {
         goto end;
      }

      if (as != MP_NO) {
         res = mp_init(&acpy);
         if (res != MP_OKAY) {
            goto end;
         }

         res = mp_add(mx, a, &acpy);
         if (res != MP_OKAY) {
            mp_clear(&acpy);
            goto end;
         }
         a = &acpy;
      }
      if (bs != MP_NO) {
         res = mp_init(&bcpy);
         if (res != MP_OKAY) {
            goto end;
         }

         res = mp_add(mx, b, &bcpy);
         if (res != MP_OKAY) {
            mp_clear(&bcpy);
            goto end;
         }
         b = &bcpy;
      }
   }

   res = mp_xor(a, b, c);

   if ((as != bs) && (res == MP_OKAY)) {
      res = mp_sub(c, mx, c);
   }

end:
   if (a == &acpy) {
      mp_clear(&acpy);
   }

   if (b == &bcpy) {
      mp_clear(&bcpy);
   }

   if (mx == &_mx) {
      mp_clear(mx);
   }

   return res;
}
#endif

/* ref:         HEAD -> master, tag: v1.1.0 */
/* git commit:  08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
/* commit time: 2019-01-28 20:32:32 +0100 */