X-Git-Url: https://pd.if.org/git/?a=blobdiff_plain;ds=sidebyside;f=tomsfastmath%2Fsrc%2Fmisc%2Ffp_rand.c;fp=tomsfastmath%2Fsrc%2Fmisc%2Ffp_rand.c;h=01198c5c2e29a91e482f9d6b812b898769093c9c;hb=66bc25938679f1d6a1d1200f329093d82a5e99b4;hp=0000000000000000000000000000000000000000;hpb=a52ee0733f420ca20224049260d6fc5cf7d8f621;p=zpackage

diff --git a/tomsfastmath/src/misc/fp_rand.c b/tomsfastmath/src/misc/fp_rand.c
new file mode 100644
index 0000000..01198c5
--- /dev/null
+++ b/tomsfastmath/src/misc/fp_rand.c
@@ -0,0 +1,65 @@
+/* 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_private.h>
+
+#if FP_GEN_RANDOM_MAX == 0xffffffff
+  #define FP_GEN_RANDOM_SHIFT  32
+#elif FP_GEN_RANDOM_MAX == 32767
+  /* SHRT_MAX */
+  #define FP_GEN_RANDOM_SHIFT  15
+#elif FP_GEN_RANDOM_MAX == 2147483647
+  /* INT_MAX */
+  #define FP_GEN_RANDOM_SHIFT  31
+#elif !defined(FP_GEN_RANDOM_SHIFT)
+#error Thou shalt define their own valid FP_GEN_RANDOM_SHIFT
+#endif
+
+/* makes a pseudo-random int of a given size */
+static fp_digit fp_gen_random(void)
+{
+  fp_digit d = 0, msk = 0;
+  do {
+    d <<= FP_GEN_RANDOM_SHIFT;
+    d |= ((fp_digit) FP_GEN_RANDOM());
+    msk <<= FP_GEN_RANDOM_SHIFT;
+    msk |= FP_GEN_RANDOM_MAX;
+  } while ((FP_MASK & msk) != FP_MASK);
+  d &= FP_MASK;
+  return d;
+}
+
+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_gen_random();
+   } while (d == 0);
+
+   fp_add_d (a, d, a);
+
+   while (--digits > 0) {
+     fp_lshd (a, 1);
+     fp_add_d (a, fp_gen_random(), a);
+   }
+
+   return;
+
+}
+
+/* $Source$ */
+/* $Revision$ */
+/* $Date$ */