1 files changed, 51 insertions, 0 deletions
diff --git a/3/6_control/22_loop.c b/3/6_control/22_loop.c
new file mode 100644
index 0000000..73c7710
--- /dev/null
+++ b/3/6_control/22_loop.c
@@ -0,0 +1,51 @@
+#include <limits.h>
+#include <stdint.h>
+#include <stdio.h>
+// do
+//    body
+//    while (test);
+//
+// loop:
+//   body
+//   t = test;
+//   if (t)
+//      goto loop;
+
+typedef int64_t fact_t;
+
+long fact_do(long n)
+{
+    long result = 1;
+    do {
+        result *= n;
+        n = n-1;
+    } while (n > 1);
+    return result;
+}
+
+int tmult_ok(fact_t x, fact_t y)
+{
+    fact_t p = x*y;
+    return !x || p/x == y;
+}
+
+fact_t fact_do_int(size_t n)
+{
+    fact_t result = 1;
+    do {
+        if (tmult_ok(result, n)) {
+            result *= n;
+            n = n-1;
+        } else {
+            printf("would overflow this iter, n=%ld\n", n);
+            n = 0;
+        }
+    } while (n > 1);
+    return result;
+}
+
+int main(void) {
+    size_t f = 20;
+    printf("result: %ld, max: %ld, less: %d", fact_do_int(f), INT64_MAX, fact_do_int(f) < INT64_MAX);
+    return 0;
+}