add fp_rand()

it's a port of the function in libtommath

src/headers/tfm.h

@@ -317,6 +317,9 @@ const char *fp_ident(void);
 /* set to a small digit */
 void fp_set(fp_int *a, fp_digit b);
 
+/* makes a pseudo-random int of a given size */
+void fp_rand(fp_int *a, int digits);
+
 /* copy from a to b */
 #define fp_copy(a, b)      (void)(((a) != (b)) && memcpy((b), (a), sizeof(fp_int)))
 #define fp_init_copy(a, b) fp_copy(b, a)

src/misc/fp_rand.c

@@ -0,0 +1,41 @@
+/* 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>
+
+/* makes a pseudo-random int of a given size */
+
+void fp_rand(fp_int *a, int digits)
+{
+   fp_digit d;
+
+   fp_zero(a);
+   if (digits <= 0) {
+     return;
+   }
+
+   /* first place a random non-zero digit */
+   do {
+     d = ((fp_digit) abs (rand ())) & FP_MASK;
+   } while (d == 0);
+
+   fp_add_d (a, d, a);
+
+   while (--digits > 0) {
+     fp_lshd (a, 1);
+     fp_add_d (a, ((fp_digit) abs (rand ())), a);
+   }
+
+   return;
+
+}
+
+/* $Source$ */
+/* $Revision$ */
+/* $Date$ */