tests: Add an example using cycle clock counts

Close #167

Author: jserv

tests/ticks.c

@@ -0,0 +1,37 @@
+#include <inttypes.h>
+#include <stdint.h>
+#include <stdio.h>
+
+typedef uint64_t ticks;
+static inline ticks getticks(void)
+{
+    uint64_t result;
+    uint32_t l, h, h2;
+    asm volatile(
+        "rdcycleh %0\n"
+        "rdcycle %1\n"
+        "rdcycleh %2\n"
+        "sub %0, %0, %2\n"
+        "seqz %0, %0\n"
+        "sub %0, zero, %0\n"
+        "and %1, %1, %0\n"
+        : "=r"(h), "=r"(l), "=r"(h2));
+    result = (((uint64_t) h) << 32) | ((uint64_t) l);
+    return result;
+}
+
+static uint64_t fib(uint64_t n)
+{
+    if (n <= 1)
+        return n;
+    return fib(n - 1) + fib(n - 2);
+}
+
+int main()
+{
+    ticks t0 = getticks();
+    fib(19);
+    ticks t1 = getticks();
+    printf("elapsed cycle: %" PRIu64 "\n", t1 - t0);
+    return 0;
+}