> The header stores only 4 bytes for crc, so it is quite reasonable.

Then I would suggest something like this, though it could be made more
efficient.

--- orig/configure.ac
+++ mod/configure.ac
@@ -51,6 +51,9 @@
 AC_CHECK_TYPE(gid_t, int)
 AC_HEADER_STDC
 AC_HEADER_DIRENT
+AC_CHECK_TYPES(uint32_t)
+AC_CHECK_SIZEOF(unsigned long)
+AC_CHECK_SIZEOF(unsigned int)
 
 AC_CHECK_FUNCS([fchmod fchown])
 # This is needed for mingw build
--- orig/src/extern.h
+++ mod/src/extern.h
@@ -66,7 +66,17 @@
 extern int archive_des;
 extern char *archive_name;
 extern char *rsh_command_option;
+#ifdef HAVE_UINT32_T
+extern uint32_t crc;
+#else
+# if SIZEOF_UNSIGNED_LONG == 4
 extern unsigned long crc;
+# elif SIZEOF_UNSIGNED_INT == 4
+extern unsigned int crc;
+# else
+# error Wrong size for crc
+# endif
+#endif
 extern int delayed_seek_count;
 #ifdef DEBUG_CPIO
 extern int debug_flag;


--- orig/src/global.c
+++ mod/src/global.c
@@ -139,7 +139,17 @@
 char *rsh_command_option = NULL;
 
 /* CRC checksum.  */
+#ifdef HAVE_UINT32_T
+uint32_t crc;
+#else
+# if SIZEOF_UNSIGNED_LONG == 4
 unsigned long crc;
+# elif SIZEOF_UNSIGNED_INT == 4
+unsigned int crc;
+# else
+# error Wrong size for crc
+# endif
+#endif
 
 /* Input and output buffers.  */
 char *input_buffer, *output_buffer;