Add FITSint() and FITSuint(),

which cast long long to int while panicking on overflow

src/hacklib.c

@@ -1360,4 +1360,21 @@ nh_snprintf(
 
 RESTORE_WARNING_FORMAT_NONLITERAL
 
+/* cast to int or panic on overflow; use via macro */
+int
+FITSint_(lua_Integer i, const char *file, int line){
+    int ret = (int)i;
+    if (ret != i)
+        panic("Overflow at %s:%d", file, line);
+    return (int)i;
+}
+
+unsigned
+FITSuint_(unsigned long long i, const char *file, int line){
+    unsigned ret = (unsigned)i;
+    if (ret != i)
+        panic("Overflow at %s:%d", file, line);
+    return (unsigned)i;
+}
+
 /*hacklib.c*/