Diff: math/bit/fp_div_2d.c

Revision:

0:35aa5be3b78d

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/math/bit/fp_div_2d.c	Fri Jun 06 10:49:02 2014 +0000
@@ -0,0 +1,79 @@
+/* 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>
+
+/* c = a / 2**b */
+void fp_div_2d(fp_int *a, int b, fp_int *c, fp_int *d)
+{
+  fp_digit D, r, rr;
+  int      x;
+  fp_int   t;
+
+  /* if the shift count is <= 0 then we do no work */
+  if (b <= 0) {
+    fp_copy (a, c);
+    if (d != NULL) {
+      fp_zero (d);
+    }
+    return;
+  }
+
+  fp_init(&t);
+
+  /* get the remainder */
+  if (d != NULL) {
+    fp_mod_2d (a, b, &t);
+  }
+
+  /* copy */
+  fp_copy(a, c);
+
+  /* shift by as many digits in the bit count */
+  if (b >= (int)DIGIT_BIT) {
+    fp_rshd (c, b / DIGIT_BIT);
+  }
+
+  /* shift any bit count < DIGIT_BIT */
+  D = (fp_digit) (b % DIGIT_BIT);
+  if (D != 0) {
+    register fp_digit *tmpc, mask, shift;
+
+    /* mask */
+    mask = (((fp_digit)1) << D) - 1;
+
+    /* shift for lsb */
+    shift = DIGIT_BIT - D;
+
+    /* alias */
+    tmpc = c->dp + (c->used - 1);
+
+    /* carry */
+    r = 0;
+    for (x = c->used - 1; x >= 0; x--) {
+      /* get the lower  bits of this word in a temp */
+      rr = *tmpc & mask;
+
+      /* shift the current word and mix in the carry bits from the previous word */
+      *tmpc = (*tmpc >> D) | (r << shift);
+      --tmpc;
+
+      /* set the carry to the carry bits of the current word found above */
+      r = rr;
+    }
+  }
+  fp_clamp (c);
+  if (d != NULL) {
+    fp_copy (&t, d);
+  }
+}
+
+/* $Source: /cvs/libtom/tomsfastmath/src/bit/fp_div_2d.c,v $ */
+/* $Revision: 1.1 $ */
+/* $Date: 2006/12/31 21:25:53 $ */