[PATCH v2 0/6] bswap.h: Rework ntohl handling

Hi,

since the add of bswap32/64() support based on __builtin support, the usage of ntohl() macros is broken on big endian machines because the macros are always overwritten providing a swap.

The first patch in the series reverts the change and the following patches try to improve the situation by allowing to always provide an optimized version.

I've been looking at recent compiler and they manage to recognize the manual shifting and use an optimize opcode if available. The ntohl version provided by glibc already provides an "optimized" version which makes an optimisation in git almost not needed. One of the motivation behind overwriting/ providing an optimized version was to provide a macro instead of using a function call. One libc that is still providing ntohl as a function call is musl. So it might makes sense to keep it. While ntohl() is provided by the libc, the ntohll() is not. I found it only on Windows provided by winsock.h.

I haven't touched the put/get_be*() macros. gcc & clang are both smart enough to swap the content accordingly and perform a single store/ load. Only the msvc seems to strugle here and performs multiple bytes stores/ loads and shifts.

Sebastian Andrzej Siewior (6):
  Revert "bswap.h: add support for built-in bswap functions"
  bswap.h: Add support for __BYTE_ORDER__
  bswap.h: Define GIT_LITTLE_ENDIAN on msvc as little endian
  bswap.h: Always overwrite ntohl/ ntohll macros
  bswap.h: Remove optimized x86 version of bswap32/64
  bswap.h: Provide a built-in based version of bswap32/64 if possible

 compat/bswap.h | 118 ++++++++++++++++++-------------------------------
 1 file changed, 44 insertions(+), 74 deletions(-)