main: assert supported integer size, representation and conversion

Abort immediately on start if chronyd is compiled on a platform with int
shorter than 32 bits, using other representation than two's complement,
or unexpected conversion of large unsigned integers to signed.

main.c

@@ -68,6 +68,18 @@ static REF_Mode ref_mode = REF_ModeNormal;
 
 /* ================================================== */
 
+static void
+do_platform_checks(void)
+{
+  /* Require at least 32-bit integers, two's complement representation and
+     the usual implementation of conversion of unsigned integers */
+  assert(sizeof (int) >= 4);
+  assert(-1 == ~0);
+  assert((int32_t)4294967295 == (int32_t)-1);
+}
+
+/* ================================================== */
+
 static void
 delete_pidfile(void)
 {
@@ -351,6 +363,8 @@ int main
   int system_log = 1;
   int config_args = 0;
 
+  do_platform_checks();
+
   LOG_Initialise();
 
   /* Parse command line options */