+/* --- @rabin_iters@ --- *
+ *
+ * Arguments: @unsigned len@ = number of bits in value
+ *
+ * Returns: Number of iterations recommended.
+ *
+ * Use: Returns the recommended number of iterations to ensure that a
+ * number with @len@ bits is really prime.
+ */
+
+int rabin_iters(unsigned len)
+{
+ static struct {
+ unsigned b;
+ int i;
+ } *p, *q, tab[] = {
+ { 100, 27 },
+ { 150, 18 },
+ { 200, 15 },
+ { 250, 12 },
+ { 300, 9 },
+ { 350, 8 },
+ { 400, 7 },
+ { 450, 6 },
+ { 550, 5 },
+ { 650, 4 },
+ { 850, 3 },
+ { 1300, 2 }
+ };
+
+ unsigned i;
+
+ /* --- Binary search through the table --- */
+
+ p = tab;
+ q = tab + (sizeof(tab)/sizeof(tab[0]));
+ for (;;) {
+ i = (q - p) / 2;
+ if (!i)
+ break;
+ if (len >= p[i].b && len < p[i + 1].b)
+ break;
+ if (len > p[i].b)
+ p = p + i;
+ else
+ q = p + i;
+ }
+ return (p[i].i);
+}
+