userland: move more multithreading from cpp-cheat!

Convert infinite_loop.c into loop.c. Keep all examples fast by default!

userland/c/loop.c

@@ -0,0 +1,43 @@
+/* https://cirosantilli.com/linux-kernel-module-cheat#c
+ *
+ * Loop and print an integer whenever a period is reached:
+ *
+ * ....
+ * ./loop.out [max=10 [period=1]]
+ * ....
+ *
+ * * period: period for printing integers to stdout
+ *           0 means disable printing.
+ * * max:    Stop counting when max is reached.
+ *           0 means count to infinity.
+ */
+
+#include <inttypes.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+int main(int argc, char **argv) {
+    uintmax_t i, j, period, max;
+    if (argc > 1) {
+        max = strtoumax(argv[1], NULL, 10);
+    } else {
+        max = 10;
+    }
+    if (argc > 2) {
+        period = strtoumax(argv[2], NULL, 10);
+    } else {
+        period = 1;
+    }
+    i = 0;
+    j = 0;
+    while (1) {
+        if (period != 0 && i % period == 0) {
+            printf("%ju\n", j);
+            j++;
+        }
+        i++;
+        if (i == max)
+            break;
+    }
+}