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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_s_mp_mul_digs.c
parentc6a259aeeca4814a97cf6694814c63e74e4e18fa (diff)
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Import of libtommath 0.33
Diffstat (limited to 'libtommath/bn_s_mp_mul_digs.c')
-rw-r--r--libtommath/bn_s_mp_mul_digs.c87
1 files changed, 87 insertions, 0 deletions
diff --git a/libtommath/bn_s_mp_mul_digs.c b/libtommath/bn_s_mp_mul_digs.c
new file mode 100644
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+++ b/libtommath/bn_s_mp_mul_digs.c
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+#include <tommath.h>
+#ifdef BN_S_MP_MUL_DIGS_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
+ */
+
+/* multiplies |a| * |b| and only computes upto digs digits of result
+ * HAC pp. 595, Algorithm 14.12 Modified so you can control how
+ * many digits of output are created.
+ */
+int
+s_mp_mul_digs (mp_int * a, mp_int * b, mp_int * c, int digs)
+{
+ mp_int t;
+ int res, pa, pb, ix, iy;
+ mp_digit u;
+ mp_word r;
+ mp_digit tmpx, *tmpt, *tmpy;
+
+ /* can we use the fast multiplier? */
+ if (((digs) < MP_WARRAY) &&
+ MIN (a->used, b->used) <
+ (1 << ((CHAR_BIT * sizeof (mp_word)) - (2 * DIGIT_BIT)))) {
+ return fast_s_mp_mul_digs (a, b, c, digs);
+ }
+
+ if ((res = mp_init_size (&t, digs)) != MP_OKAY) {
+ return res;
+ }
+ t.used = digs;
+
+ /* compute the digits of the product directly */
+ pa = a->used;
+ for (ix = 0; ix < pa; ix++) {
+ /* set the carry to zero */
+ u = 0;
+
+ /* limit ourselves to making digs digits of output */
+ pb = MIN (b->used, digs - ix);
+
+ /* setup some aliases */
+ /* copy of the digit from a used within the nested loop */
+ tmpx = a->dp[ix];
+
+ /* an alias for the destination shifted ix places */
+ tmpt = t.dp + ix;
+
+ /* an alias for the digits of b */
+ tmpy = b->dp;
+
+ /* compute the columns of the output and propagate the carry */
+ for (iy = 0; iy < pb; iy++) {
+ /* compute the column as a mp_word */
+ r = ((mp_word)*tmpt) +
+ ((mp_word)tmpx) * ((mp_word)*tmpy++) +
+ ((mp_word) u);
+
+ /* the new column is the lower part of the result */
+ *tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK));
+
+ /* get the carry word from the result */
+ u = (mp_digit) (r >> ((mp_word) DIGIT_BIT));
+ }
+ /* set carry if it is placed below digs */
+ if (ix + iy < digs) {
+ *tmpt = u;
+ }
+ }
+
+ mp_clamp (&t);
+ mp_exch (&t, c);
+
+ mp_clear (&t);
+ return MP_OKAY;
+}
+#endif