rem: physmem_available ()
add: physmem_available (void)
context: physmem_available (){#if defined _SC_AVPHYS_PAGES && defined _SC_PAGESIZE  { /* This works on linux-gnu, solaris2 and cygwin.  */    double pages = sysconf (_SC_AVPHYS_PAGES);    double pagesize = sysconf (_SC_PAGESIZE);    if (0 <= pages && 0 <= pagesize)      return pages * pagesize;  }#endif#if HAVE_PSTAT_GETSTATIC && HAVE_PSTAT_GETDYNAMIC  { /* This works on hpux11.  */    struct pst_static pss;    struct pst_dynamic psd;    if (0 <= pstat_getstatic (&pss, sizeof pss, 1, 0)	&& 0 <= pstat_getdynamic (&psd, sizeof psd, 1, 0))      {	double pages = psd.psd_free;	double pagesize = pss.page_size;	if (0 <= pages && 0 <= pagesize)	  return pages * pagesize;      }  }#endif#if HAVE_SYSMP && defined MP_SAGET && defined MPSA_RMINFO && defined _SC_PAGESIZE  { /* This works on irix6. */    struct rminfo realmem;    if (sysmp (MP_SAGET, MPSA_RMINFO, &realmem, sizeof realmem) == 0)      {	double pagesize = sysconf (_SC_PAGESIZE);	double pages = realmem.availrmem;	if (0 <= pages && 0 <= pagesize)	  return pages * pagesize;      }  }#endif#if HAVE_TABLE && defined TBL_VMSTATS  { /* This works on Tru64 UNIX V4/5.  */    struct tbl_vmstats vmstats;    if (table (TBL_VMSTATS, 0, &vmstats, 1, sizeof (vmstats)) == 1)      {	double pages = vmstats.free_count;	double pagesize = vmstats.pagesize;	if (0 <= pages && 0 <= pagesize)	  return pages * pagesize;      }  }#endif#if HAVE_SYSCTL && defined HW_USERMEM  { /* This works on *bsd and darwin.  */    unsigned int usermem;    size_t len = sizeof usermem;    static int mib[2] = { CTL_HW, HW_USERMEM };    if (sysctl (mib, ARRAY_SIZE (mib), &usermem, &len, NULL, 0) == 0	&& len == sizeof (usermem))      return (double) usermem;  }#endif#if defined _WIN32  { /* this works on windows */    PFN_MS_EX pfnex;    HMODULE h = GetModuleHandle ("kernel32.dll");    if (!h)      return 0.0;    /*  Use GlobalMemoryStatusEx if available.  */    if ((pfnex = (PFN_MS_EX) GetProcAddress (h, "GlobalMemoryStatusEx")))      {	lMEMORYSTATUSEX lms_ex;	lms_ex.dwLength = sizeof lms_ex;	if (!pfnex (&lms_ex))	  return 0.0;	return (double) lms_ex.ullAvailPhys;      }    /*  Fall back to GlobalMemoryStatus which is always available.        but returns wrong results for physical memory > 4GB  */    else      {	MEMORYSTATUS ms;	GlobalMemoryStatus (&ms);	return (double) ms.dwAvailPhys;      }  }#endif  /* Guess 25% of physical memory.  */  return physmem_total () / 4;}