static char *committed = NULL;      /* XXX threadead */
static char *base      = NULL;      /* XXX threadead */
static char *reserved  = NULL;      /* XXX threadead */
static char *brk       = NULL;      /* XXX threadead */
static DWORD pagesize  = 0;     /* XXX threadead */

void *
sbrk(ptrdiff_t need)
{
 void *result;
 if (!pagesize)
  {SYSTEM_INFO info;
   GetSystemInfo(&info);
   /* Pretend page size is larger so we don't perpetually
    * call the OS to commit just one page ...
    */
   pagesize = info.dwPageSize << 3;
  }
 if (brk+need >= reserved)
  {
   DWORD size = brk+need-reserved;
   char *addr;
   char *prev_committed = NULL;
   if (committed && reserved && committed < reserved)
    {
     /* Commit last of previous chunk cannot span allocations */
     addr = (char *) VirtualAlloc(committed,reserved-committed,MEM_COMMIT,PAGE_READWRITE);
     if (addr)
      {
      /* Remember where we committed from in case we want to decommit later */
      prev_committed = committed;
      committed = reserved;
      }
    }
   /* Reserve some (more) space
    * Contiguous blocks give us greater efficiency, so reserve big blocks -
    * this is only address space not memory...
    * Note this is a little sneaky, 1st call passes NULL as reserved
    * so lets system choose where we start, subsequent calls pass
    * the old end address so ask for a contiguous block
    */
sbrk_reserve:
   if (size < 64*1024*1024)
    size = 64*1024*1024;
   size = ((size + pagesize - 1) / pagesize) * pagesize;
   addr  = (char *) VirtualAlloc(reserved,size,MEM_RESERVE,PAGE_NOACCESS);
   if (addr)
    {
     reserved = addr+size;
     if (!base)
      base = addr;
     if (!committed)
      committed = base;
     if (!brk)
      brk = committed;
    }
   else if (reserved)
    {
      /* The existing block could not be extended far enough, so decommit
       * anything that was just committed above and start anew */
      if (prev_committed)
       {
       if (!VirtualFree(prev_committed,reserved-prev_committed,MEM_DECOMMIT))
        return (void *) -1;
       }
      reserved = base = committed = brk = NULL;
      size = need;
      goto sbrk_reserve;
    }
   else
    {
     return (void *) -1;
    }
  }
 result = brk;
 brk += need;
 if (brk > committed)
  {
   DWORD size = ((brk-committed + pagesize -1)/pagesize) * pagesize;
   char *addr;
   if (committed+size > reserved)
    size = reserved-committed;
   addr = (char *) VirtualAlloc(committed,size,MEM_COMMIT,PAGE_READWRITE);
   if (addr)
    committed += size;
   else
    return (void *) -1;
  }
 return result;
}