Diff: math/bit/fp_div_2.c

Revision:

0:35aa5be3b78d

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/math/bit/fp_div_2.c	Fri Jun 06 10:49:02 2014 +0000
@@ -0,0 +1,53 @@
+/* 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>
+
+/* b = a/2 */
+void fp_div_2(fp_int * a, fp_int * b)
+{
+  int     x, oldused;
+
+  oldused = b->used;
+  b->used = a->used;
+  {
+    register fp_digit r, rr, *tmpa, *tmpb;
+
+    /* source alias */
+    tmpa = a->dp + b->used - 1;
+
+    /* dest alias */
+    tmpb = b->dp + b->used - 1;
+
+    /* carry */
+    r = 0;
+    for (x = b->used - 1; x >= 0; x--) {
+      /* get the carry for the next iteration */
+      rr = *tmpa & 1;
+
+      /* shift the current digit, add in carry and store */
+      *tmpb-- = (*tmpa-- >> 1) | (r << (DIGIT_BIT - 1));
+
+      /* forward carry to next iteration */
+      r = rr;
+    }
+
+    /* zero excess digits */
+    tmpb = b->dp + b->used;
+    for (x = b->used; x < oldused; x++) {
+      *tmpb++ = 0;
+    }
+  }
+  b->sign = a->sign;
+  fp_clamp (b);
+}
+
+/* $Source: /cvs/libtom/tomsfastmath/src/bit/fp_div_2.c,v $ */
+/* $Revision: 1.1 $ */
+/* $Date: 2006/12/31 21:25:53 $ */