### diff libtommath/bn_mp_mul_2d.c @ 389:5ff8218bcee9

author Matt Johnston Thu, 11 Jan 2007 03:14:55 +0000 eed26cff980b 60fc6476e044
line wrap: on
line diff
```--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtommath/bn_mp_mul_2d.c	Thu Jan 11 03:14:55 2007 +0000
@@ -0,0 +1,85 @@
+#include <tommath.h>
+#ifdef BN_MP_MUL_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, [email protected], http://math.libtomcrypt.com
+ */
+
+/* shift left by a certain bit count */
+int mp_mul_2d (mp_int * a, int b, mp_int * c)
+{
+  mp_digit d;
+  int      res;
+
+  /* copy */
+  if (a != c) {
+     if ((res = mp_copy (a, c)) != MP_OKAY) {
+       return res;
+     }
+  }
+
+  if (c->alloc < (int)(c->used + b/DIGIT_BIT + 1)) {
+     if ((res = mp_grow (c, c->used + b / DIGIT_BIT + 1)) != MP_OKAY) {
+       return res;
+     }
+  }
+
+  /* shift by as many digits in the bit count */
+  if (b >= (int)DIGIT_BIT) {
+    if ((res = mp_lshd (c, b / DIGIT_BIT)) != MP_OKAY) {
+      return res;
+    }
+  }
+
+  /* shift any bit count < DIGIT_BIT */
+  d = (mp_digit) (b % DIGIT_BIT);
+  if (d != 0) {
+    register mp_digit *tmpc, shift, mask, r, rr;
+    register int x;
+
+    /* bitmask for carries */
+    mask = (((mp_digit)1) << d) - 1;
+
+    /* shift for msbs */
+    shift = DIGIT_BIT - d;
+
+    /* alias */
+    tmpc = c->dp;
+
+    /* carry */
+    r    = 0;
+    for (x = 0; x < c->used; x++) {
+      /* get the higher bits of the current word */
+      rr = (*tmpc >> shift) & mask;
+
+      /* shift the current word and OR in the carry */
+      *tmpc = ((*tmpc << d) | r) & MP_MASK;
+      ++tmpc;
+
+      /* set the carry to the carry bits of the current word */
+      r = rr;
+    }
+
+    /* set final carry */
+    if (r != 0) {
+       c->dp[(c->used)++] = r;
+    }
+  }
+  mp_clamp (c);
+  return MP_OKAY;
+}
+#endif
+
+/* \$Source: /cvs/libtom/libtommath/bn_mp_mul_2d.c,v \$ */
+/* \$Revision: 1.3 \$ */
+/* \$Date: 2006/03/31 14:18:44 \$ */```