1 files changed, 51 insertions, 42 deletions
diff --git a/libtommath/bn_mp_xor.c b/libtommath/bn_mp_xor.c
index 432f42e..fba6617 100644
--- a/libtommath/bn_mp_xor.c
+++ b/libtommath/bn_mp_xor.c
@@ -1,47 +1,56 @@
 #include <tommath.h>
 #ifdef BN_MP_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.
- *
- * The library is free for all purposes without any express
- * guarantee it works.
- *
- * Tom St Denis, tomstdenis@gmail.com, http://math.libtomcrypt.com
- */
-
-/* XOR two ints together */
-int
-mp_xor (mp_int * a, mp_int * b, mp_int * c)
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+/* two complement xor */
+mp_err mp_xor(const mp_int *a, const mp_int *b, mp_int *c)
 {
-  int     res, ix, px;
-  mp_int  t, *x;
-
-  if (a->used > b->used) {
-    if ((res = mp_init_copy (&t, a)) != MP_OKAY) {
-      return res;
-    }
-    px = b->used;
-    x = b;
-  } else {
-    if ((res = mp_init_copy (&t, b)) != MP_OKAY) {
-      return res;
-    }
-    px = a->used;
-    x = a;
-  }
-
-  for (ix = 0; ix < px; ix++) {
-     t.dp[ix] ^= x->dp[ix];
-  }
-  mp_clamp (&t);
-  mp_exch (c, &t);
-  mp_clear (&t);
-  return MP_OKAY;
+   int used = MAX(a->used, b->used) + 1, i;
+   mp_err err;
+   mp_digit ac = 1, bc = 1, cc = 1;
+   mp_sign csign = (a->sign != b->sign) ? MP_NEG : MP_ZPOS;
+
+   if (c->alloc < used) {
+      if ((err = mp_grow(c, used)) != MP_OKAY) {
+         return err;
+      }
+   }
+
+   for (i = 0; i < used; i++) {
+      mp_digit x, y;
+
+      /* convert to two complement if negative */
+      if (a->sign == MP_NEG) {
+         ac += (i >= a->used) ? MP_MASK : (~a->dp[i] & MP_MASK);
+         x = ac & MP_MASK;
+         ac >>= MP_DIGIT_BIT;
+      } else {
+         x = (i >= a->used) ? 0uL : a->dp[i];
+      }
+
+      /* convert to two complement if negative */
+      if (b->sign == MP_NEG) {
+         bc += (i >= b->used) ? MP_MASK : (~b->dp[i] & MP_MASK);
+         y = bc & MP_MASK;
+         bc >>= MP_DIGIT_BIT;
+      } else {
+         y = (i >= b->used) ? 0uL : b->dp[i];
+      }
+
+      c->dp[i] = x ^ y;
+
+      /* convert to to sign-magnitude if negative */
+      if (csign == MP_NEG) {
+         cc += ~c->dp[i] & MP_MASK;
+         c->dp[i] = cc & MP_MASK;
+         cc >>= MP_DIGIT_BIT;
+      }
+   }
+
+   c->used = used;
+   c->sign = csign;
+   mp_clamp(c);
+   return MP_OKAY;
 }
 #endif