Make byteswap functions portable so that sflowtool can build on Mac

[ravd]

No description provided.

[sflow]

I don't have the Xcode build tools installed on my Mac, but I think the right way to do this it to edit configure.ac and add byteswap.h to the AC_CHECK_HEADERS list. That will cause HAVE_BYTESWAP_H to be set to 1 or 0 in config.h when you rebuild. And then you can do something like this in sflowtool.c:

#if HAVE_BYTESWAP_H
#include <byteswap.h>
#else
#define bswap_16 __builtin_bswap_16
#define bswap_32 __builtin_bswap_32
#define bswap_64 __builtin_bswap_64
#endif

Or use the code you suggested if those builtins do not exist (I didn't check any of this).

Having said all that, I suggest you just run sflowtool under docker. It's more likely to work as expected, and the overhead is small. Just try this:

docker run sflowtool

[sflow]

I finally got around to trying this properly, and of course I learned that _builtin_bswap* is not known to the compiler on macOS. So the latest sflowtool.c includes something closer to what was proposed. Please review when you have time. It looks like this:

#if HAVE_BYTESWAP_H
#include <byteswap.h>
#else
#define bswap_16(value)
((((value) & 0xff) << 8) | ((value) >> 8))

#define bswap_32(value)
(((uint32_t)bswap_16((uint16_t)((value) & 0xffff)) << 16) |
(uint32_t)bswap_16((uint16_t)((value) >> 16)))

#define bswap_64(value)
(((uint64_t)bswap_32((uint32_t)((value) & 0xffffffff)) << 32) |
(uint64_t)bswap_32((uint32_t)((value) >> 32)))
#endif