Diff: math/mul/fp_mul_2.c

Revision:

0:35aa5be3b78d

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/math/mul/fp_mul_2.c	Fri Jun 06 10:49:02 2014 +0000
@@ -0,0 +1,67 @@
+/* TomsFastMath, a fast ISO C bignum library.
+ * 
+ * This project is meant to fill in where LibTomMath
+ * falls short.  That is speed ;-)
+ *
+ * This project is public domain and free for all purposes.
+ * 
+ * Tom St Denis, tomstdenis@gmail.com
+ */
+#include <tfm.h>
+
+void fp_mul_2(fp_int * a, fp_int * b)
+{
+  int     x, oldused;
+   
+  oldused = b->used;
+  b->used = a->used;
+
+  {
+    register fp_digit r, rr, *tmpa, *tmpb;
+
+    /* alias for source */
+    tmpa = a->dp;
+    
+    /* alias for dest */
+    tmpb = b->dp;
+
+    /* carry */
+    r = 0;
+    for (x = 0; x < a->used; x++) {
+    
+      /* get what will be the *next* carry bit from the 
+       * MSB of the current digit 
+       */
+      rr = *tmpa >> ((fp_digit)(DIGIT_BIT - 1));
+      
+      /* now shift up this digit, add in the carry [from the previous] */
+      *tmpb++ = ((*tmpa++ << ((fp_digit)1)) | r);
+      
+      /* copy the carry that would be from the source 
+       * digit into the next iteration 
+       */
+      r = rr;
+    }
+
+    /* new leading digit? */
+    if (r != 0 && b->used != (FP_SIZE-1)) {
+      /* add a MSB which is always 1 at this point */
+      *tmpb = 1;
+      ++(b->used);
+    }
+
+    /* now zero any excess digits on the destination 
+     * that we didn't write to 
+     */
+    tmpb = b->dp + b->used;
+    for (x = b->used; x < oldused; x++) {
+      *tmpb++ = 0;
+    }
+  }
+  b->sign = a->sign;
+}
+
+
+/* $Source: /cvs/libtom/tomsfastmath/src/mul/fp_mul_2.c,v $ */
+/* $Revision: 1.1 $ */
+/* $Date: 2006/12/31 21:25:53 $ */