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// return free and total system memory in bytes 
uint64_t I_GetFreeMem(uint64_t *total)
{
#ifdef LINUX
  // LINUX covers all the unix-type OS's.
 
#ifdef FREEBSD
    struct  vmmeter sum;
    kvm_t *kd;
    struct nlist namelist[]= {
#define X_SUM   0
    {"_cnt"},
    { NULL }
    };
    if ((kd = kvm_open(NULL, NULL, NULL, O_RDONLY, "kvm_open")) == NULL)
      goto guess;
 
    if (kvm_nlist(kd, namelist) != 0)
    {
    kvm_close (kd);
    goto guess;
    }
    if (kvm_read(kd,namelist[X_SUM].n_value ,&sum, sizeof(sum)) != sizeof(sum))
    {
    kvm_close (kd);
    goto guess;
    }
    kvm_close (kd);
 
    *total = sum.v_page_count * sum.v_page_size;
    return sum.v_free_count * sum.v_page_size;
#elif defined(SOLARIS)
    goto guess;
#else
    // Actual Linux
 
#define MEMINFO_FILE "/proc/meminfo"
#define MEMTOTAL "MemTotal:"
#define MEMFREE "MemFree:"
 
    char buf[1024];    
    char *memTag;
    uint64_t freeKBytes;
    uint64_t totalKBytes;
 
    int meminfo_fd = open(MEMINFO_FILE, O_RDONLY);
    int n = read(meminfo_fd, buf, 1023);
    close(meminfo_fd);
    
    if(n<0)
      goto guess;
    
    buf[n] = '\0';
    if(NULL == (memTag = strstr(buf, MEMTOTAL)))
      goto guess;
        
    memTag += sizeof(MEMTOTAL);
    totalKBytes = atoi(memTag);
    
    if(NULL == (memTag = strstr(buf, MEMFREE)))
      goto guess;
        
    memTag += sizeof(MEMFREE);
    freeKBytes = atoi(memTag);
    
    *total = totalKBytes << 10;
    return freeKBytes << 10;
 guess:
  // make a conservative guess
  *total = 32 << 20;
  return   32 << 20;
#endif // Unix flavors
#elif defined(WIN32)
  // windows
#if defined(WIN_LARGE_MEM) && defined( _WIN32_WINNT ) && (_WIN32_WINNT >= 0x0500)
  // large memory status, only in newer libraries
  MEMORYSTATUSEX statex;
  statex.dwLength = sizeof(statex);
  GlobalMemoryStatusEx(&statex);
  *total = statex.ullTotalPhys;
  return statex.ullAvailPhys;
#else
  // older memory status
  MEMORYSTATUS statex;
  statex.dwLength = sizeof(statex);
  GlobalMemoryStatus(&statex);
  *total = statex.dwTotalPhys;
  return statex.dwAvailPhys;
#endif
 
#else
  // unknown
  // make a conservative guess
  *total = 32 << 20;
  return   32 << 20;
#endif
 
}