* libtommath/bn_mp_add_d.c: Bug fix. For mp_add_d(&a, d, &c),

        when &a has the value -d, then the value &c computed should be zero,
        but mp_add_d was producing an inconsistent zero value with a sign
        field of MP_NEG, something like a value of -0, which other routines
        in libtommath can't handle.

2 files changed, 112 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index c23d7e4..8df0368 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -7,6 +7,12 @@
 	* win/Makefile.in:
 	* win/makefile.vc:
 
+	* libtommath/bn_mp_add_d.c:	Bug fix.  For mp_add_d(&a, d, &c),
+	when &a has the value -d, then the value &c computed should be zero,
+	but mp_add_d was producing an inconsistent zero value with a sign
+	field of MP_NEG, something like a value of -0, which other routines
+	in libtommath can't handle.
+
 	* generic/tclExecute.c:	Dropped all creation of "bigOne" values
 	and just use tommath routines that accept the value "1" directly.
 
diff --git a/libtommath/bn_mp_add_d.c b/libtommath/bn_mp_add_d.c
new file mode 100644
index 0000000..bf9f4bc
--- /dev/null
+++ b/libtommath/bn_mp_add_d.c
@@ -0,0 +1,106 @@
+#include <tommath.h>
+#ifdef BN_MP_ADD_D_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@iahu.ca, http://math.libtomcrypt.org
+ */
+
+/* single digit addition */
+int
+mp_add_d (mp_int * a, mp_digit b, mp_int * c)
+{
+  int     res, ix, oldused;
+  mp_digit *tmpa, *tmpc, mu;
+
+  /* grow c as required */
+  if (c->alloc < a->used + 1) {
+     if ((res = mp_grow(c, a->used + 1)) != MP_OKAY) {
+        return res;
+     }
+  }
+
+  /* if a is negative and |a| >= b, call c = |a| - b */
+  if (a->sign == MP_NEG && (a->used > 1 || a->dp[0] >= b)) {
+     /* temporarily fix sign of a */
+     a->sign = MP_ZPOS;
+
+     /* c = |a| - b */
+     res = mp_sub_d(a, b, c);
+
+     /* fix signs  */
+     a->sign = MP_NEG;
+     c->sign = (c->used) ? MP_NEG : MP_ZPOS;
+
+     return res;
+  }
+
+  /* old number of used digits in c */
+  oldused = c->used;
+
+  /* sign always positive */
+  c->sign = MP_ZPOS;
+
+  /* source alias */
+  tmpa    = a->dp;
+
+  /* destination alias */
+  tmpc    = c->dp;
+
+  /* if a is positive */
+  if (a->sign == MP_ZPOS) {
+     /* add digit, after this we're propagating
+      * the carry.
+      */
+     *tmpc   = *tmpa++ + b;
+     mu      = *tmpc >> DIGIT_BIT;
+     *tmpc++ &= MP_MASK;
+
+     /* now handle rest of the digits */
+     for (ix = 1; ix < a->used; ix++) {
+        *tmpc   = *tmpa++ + mu;
+        mu      = *tmpc >> DIGIT_BIT;
+        *tmpc++ &= MP_MASK;
+     }
+     /* set final carry */
+     ix++;
+     *tmpc++  = mu;
+
+     /* setup size */
+     c->used = a->used + 1;
+  } else {
+     /* a was negative and |a| < b */
+     c->used  = 1;
+
+     /* the result is a single digit */
+     if (a->used == 1) {
+        *tmpc++  =  b - a->dp[0];
+     } else {
+        *tmpc++  =  b;
+     }
+
+     /* setup count so the clearing of oldused
+      * can fall through correctly
+      */
+     ix       = 1;
+  }
+
+  /* now zero to oldused */
+  while (ix++ < oldused) {
+     *tmpc++ = 0;
+  }
+  mp_clamp(c);
+
+  return MP_OKAY;
+}
+
+#endif