Unittest replacement function in library

Suppose that you need to implement a replacement function, for instance be64toh which was added in glibc-2.9, to remain compatible with legacy system. Ofcourse you want to use the real function if available.

Function implementation

The replacement is called _int_be64toh and the header conditionally aliases be64toh to _int_be64toh. This way it is possible to compile on any system without any interference. It might be a good idea to adjust the visibility of the function as well.

Code: be64toh.h (view, download)

1. #ifndef __WORKAROUND_BE64TOH_H
2. #define __WORKAROUND_BE64TOH_H
3.  
4. #include <stdint.h>
5.  
6. #ifdef HAVE_BE64TOH
7. #include <endian.h>
8. #else
9.  
10. uint64_t be64toh(uint64_t val) __attribute__((weakref("_int_be64toh")));
11.  
12. #endif /* HAVE_BE64TOH */
13.  
14. #endif /* __WORKAROUND_BE64TOH_H */

Code: be64toh.c (view, download)

1. #ifdef HAVE_CONFIG_H
2. #include "config.h"
3. #endif /* HAVE_CONFIG_H */
4.  
5. #include "be64toh.h"
6. #include <arpa/inet.h>
7.  
8. union bits {
9.         uint32_t v[2];
10.         uint64_t d;
11. };
12.  
13. uint64_t _int_be64toh(uint64_t big_endian_64bits){
14.         union bits out, in = { .d = big_endian_64bits };
15.  
16.         out.v[1] = ntohl(in.v[0]);
17.         out.v[0] = ntohl(in.v[1]);
18.  
19.         return out.d;
20. }

Conditional compilation

(Not showing the configure test, it varies too much depending on context)

Code: Makefile.am (view, download)

1. if BUILD_BE64TOH
2. libfoo_la_SOURCES += be64toh.c be64toh.h
3. endif
4.  
5. tests_bar_CFLAGS = ${AM_CFLAGS} -Dfulhack
6. tests_bar_LDADD = libfoo.la
7. tests_bar_SOURCES = tests/bar.c be64toh.c

-Dfulhack (or anything similar) is needed or you get

 Makefile.am: object `be64toh.$(OBJEXT)' created both with libtool and without

Unittest

Now you can use _int_be64toh in you unittests (if you want to compare the result with the system implementation, which is a good idea, you can only run the test if HAVE_BE64TOH is defined.)