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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_div_d.c
parentc6a259aeeca4814a97cf6694814c63e74e4e18fa (diff)
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Import of libtommath 0.33
Diffstat (limited to 'libtommath/bn_mp_div_d.c')
-rw-r--r--libtommath/bn_mp_div_d.c106
1 files changed, 106 insertions, 0 deletions
diff --git a/libtommath/bn_mp_div_d.c b/libtommath/bn_mp_div_d.c
new file mode 100644
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--- /dev/null
+++ b/libtommath/bn_mp_div_d.c
@@ -0,0 +1,106 @@
+#include <tommath.h>
+#ifdef BN_MP_DIV_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
+ */
+
+static int s_is_power_of_two(mp_digit b, int *p)
+{
+ int x;
+
+ for (x = 1; x < DIGIT_BIT; x++) {
+ if (b == (((mp_digit)1)<<x)) {
+ *p = x;
+ return 1;
+ }
+ }
+ return 0;
+}
+
+/* single digit division (based on routine from MPI) */
+int mp_div_d (mp_int * a, mp_digit b, mp_int * c, mp_digit * d)
+{
+ mp_int q;
+ mp_word w;
+ mp_digit t;
+ int res, ix;
+
+ /* cannot divide by zero */
+ if (b == 0) {
+ return MP_VAL;
+ }
+
+ /* quick outs */
+ if (b == 1 || mp_iszero(a) == 1) {
+ if (d != NULL) {
+ *d = 0;
+ }
+ if (c != NULL) {
+ return mp_copy(a, c);
+ }
+ return MP_OKAY;
+ }
+
+ /* power of two ? */
+ if (s_is_power_of_two(b, &ix) == 1) {
+ if (d != NULL) {
+ *d = a->dp[0] & ((((mp_digit)1)<<ix) - 1);
+ }
+ if (c != NULL) {
+ return mp_div_2d(a, ix, c, NULL);
+ }
+ return MP_OKAY;
+ }
+
+#ifdef BN_MP_DIV_3_C
+ /* three? */
+ if (b == 3) {
+ return mp_div_3(a, c, d);
+ }
+#endif
+
+ /* no easy answer [c'est la vie]. Just division */
+ if ((res = mp_init_size(&q, a->used)) != MP_OKAY) {
+ return res;
+ }
+
+ q.used = a->used;
+ q.sign = a->sign;
+ w = 0;
+ for (ix = a->used - 1; ix >= 0; ix--) {
+ w = (w << ((mp_word)DIGIT_BIT)) | ((mp_word)a->dp[ix]);
+
+ if (w >= b) {
+ t = (mp_digit)(w / b);
+ w -= ((mp_word)t) * ((mp_word)b);
+ } else {
+ t = 0;
+ }
+ q.dp[ix] = (mp_digit)t;
+ }
+
+ if (d != NULL) {
+ *d = (mp_digit)w;
+ }
+
+ if (c != NULL) {
+ mp_clamp(&q);
+ mp_exch(&q, c);
+ }
+ mp_clear(&q);
+
+ return res;
+}
+
+#endif