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authorKevin B Kenny <kennykb@acm.org>2005-01-19 22:41:26 (GMT)
committerKevin B Kenny <kennykb@acm.org>2005-01-19 22:41:26 (GMT)
commitb9cf65a08e6a59e434685e894e3189c201ac6791 (patch)
tree1f0868ef44c9f17d83d10dc94343df7b8cfe1842 /libtommath/bn_mp_add_d.c
parentc6a259aeeca4814a97cf6694814c63e74e4e18fa (diff)
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Import of libtommath 0.33
Diffstat (limited to 'libtommath/bn_mp_add_d.c')
-rw-r--r--libtommath/bn_mp_add_d.c105
1 files changed, 105 insertions, 0 deletions
diff --git a/libtommath/bn_mp_add_d.c b/libtommath/bn_mp_add_d.c
new file mode 100644
index 0000000..bdd0280
--- /dev/null
+++ b/libtommath/bn_mp_add_d.c
@@ -0,0 +1,105 @@
+#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 sign */
+ a->sign = c->sign = MP_NEG;
+
+ 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