[geeks] porting OSX C++ to linux

[Joshua D Boyd]

I have a program that compiles on OSX (allegedly), and win32, but two
of it's files won't compile under linux (with GCC 2.95.4).

They both complain about a missing function.  Apparently, on win32,
visuall c++ has it built in, but gcc on osx requires these lines:
#if project_builder	 
// If your system doesn't have a rotate function for 32 bits integers,
// then define it thus:
static unsigned long _lrotl (unsigned long x, int r) {
  return (x << r) | (x >> (sizeof(x)*8-r));}
#endif

What would be the proper way to #if that is that it is true for both
OSX and linux?  I must admit, my experience with cross platform
projects is pretty minimal.  When faced with it, I seperate all my N
platforms into N+1 directories (where the N+1th directory is for
platform neutral stuff), then try to place as much of the logic as
possible in the N+1th directory, rather than everything sharing one
codebase. 

-- 
Joshua D. Boyd