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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)
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tree47f8ad0d7291237c7f9af988c5e05275ed9286ee /libtommath/bn_mp_div_2d.c
parentb23d942a1e86ddee18c2309afd7fa7e9afa79ef8 (diff)
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Import of libtommath 0.33
Diffstat (limited to 'libtommath/bn_mp_div_2d.c')
-rw-r--r--libtommath/bn_mp_div_2d.c93
1 files changed, 93 insertions, 0 deletions
diff --git a/libtommath/bn_mp_div_2d.c b/libtommath/bn_mp_div_2d.c
new file mode 100644
index 0000000..cf103f2
--- /dev/null
+++ b/libtommath/bn_mp_div_2d.c
@@ -0,0 +1,93 @@
+#include <tommath.h>
+#ifdef BN_MP_DIV_2D_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
+ */
+
+/* shift right by a certain bit count (store quotient in c, optional remainder in d) */
+int mp_div_2d (mp_int * a, int b, mp_int * c, mp_int * d)
+{
+ mp_digit D, r, rr;
+ int x, res;
+ mp_int t;
+
+
+ /* if the shift count is <= 0 then we do no work */
+ if (b <= 0) {
+ res = mp_copy (a, c);
+ if (d != NULL) {
+ mp_zero (d);
+ }
+ return res;
+ }
+
+ if ((res = mp_init (&t)) != MP_OKAY) {
+ return res;
+ }
+
+ /* get the remainder */
+ if (d != NULL) {
+ if ((res = mp_mod_2d (a, b, &t)) != MP_OKAY) {
+ mp_clear (&t);
+ return res;
+ }
+ }
+
+ /* copy */
+ if ((res = mp_copy (a, c)) != MP_OKAY) {
+ mp_clear (&t);
+ return res;
+ }
+
+ /* shift by as many digits in the bit count */
+ if (b >= (int)DIGIT_BIT) {
+ mp_rshd (c, b / DIGIT_BIT);
+ }
+
+ /* shift any bit count < DIGIT_BIT */
+ D = (mp_digit) (b % DIGIT_BIT);
+ if (D != 0) {
+ register mp_digit *tmpc, mask, shift;
+
+ /* mask */
+ mask = (((mp_digit)1) << D) - 1;
+
+ /* shift for lsb */
+ shift = DIGIT_BIT - D;
+
+ /* alias */
+ tmpc = c->dp + (c->used - 1);
+
+ /* carry */
+ r = 0;
+ for (x = c->used - 1; x >= 0; x--) {
+ /* get the lower bits of this word in a temp */
+ rr = *tmpc & mask;
+
+ /* shift the current word and mix in the carry bits from the previous word */
+ *tmpc = (*tmpc >> D) | (r << shift);
+ --tmpc;
+
+ /* set the carry to the carry bits of the current word found above */
+ r = rr;
+ }
+ }
+ mp_clamp (c);
+ if (d != NULL) {
+ mp_exch (&t, d);
+ }
+ mp_clear (&t);
+ return MP_OKAY;
+}
+#endif