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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)
commitef78ca64ce6ba6a8786f083318fe536f2bd52925 (patch)
tree47f8ad0d7291237c7f9af988c5e05275ed9286ee /libtommath/bn_mp_sub_d.c
parentb23d942a1e86ddee18c2309afd7fa7e9afa79ef8 (diff)
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Import of libtommath 0.33
Diffstat (limited to 'libtommath/bn_mp_sub_d.c')
-rw-r--r--libtommath/bn_mp_sub_d.c85
1 files changed, 85 insertions, 0 deletions
diff --git a/libtommath/bn_mp_sub_d.c b/libtommath/bn_mp_sub_d.c
new file mode 100644
index 0000000..4923dde
--- /dev/null
+++ b/libtommath/bn_mp_sub_d.c
@@ -0,0 +1,85 @@
+#include <tommath.h>
+#ifdef BN_MP_SUB_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 subtraction */
+int
+mp_sub_d (mp_int * a, mp_digit b, mp_int * c)
+{
+ mp_digit *tmpa, *tmpc, mu;
+ int res, ix, oldused;
+
+ /* 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 just do an unsigned
+ * addition [with fudged signs]
+ */
+ if (a->sign == MP_NEG) {
+ a->sign = MP_ZPOS;
+ res = mp_add_d(a, b, c);
+ a->sign = c->sign = MP_NEG;
+ return res;
+ }
+
+ /* setup regs */
+ oldused = c->used;
+ tmpa = a->dp;
+ tmpc = c->dp;
+
+ /* if a <= b simply fix the single digit */
+ if ((a->used == 1 && a->dp[0] <= b) || a->used == 0) {
+ if (a->used == 1) {
+ *tmpc++ = b - *tmpa;
+ } else {
+ *tmpc++ = b;
+ }
+ ix = 1;
+
+ /* negative/1digit */
+ c->sign = MP_NEG;
+ c->used = 1;
+ } else {
+ /* positive/size */
+ c->sign = MP_ZPOS;
+ c->used = a->used;
+
+ /* subtract first digit */
+ *tmpc = *tmpa++ - b;
+ mu = *tmpc >> (sizeof(mp_digit) * CHAR_BIT - 1);
+ *tmpc++ &= MP_MASK;
+
+ /* handle rest of the digits */
+ for (ix = 1; ix < a->used; ix++) {
+ *tmpc = *tmpa++ - mu;
+ mu = *tmpc >> (sizeof(mp_digit) * CHAR_BIT - 1);
+ *tmpc++ &= MP_MASK;
+ }
+ }
+
+ /* zero excess digits */
+ while (ix++ < oldused) {
+ *tmpc++ = 0;
+ }
+ mp_clamp(c);
+ return MP_OKAY;
+}
+
+#endif