_xseek64
extern off64_t _xseek64(FILE *iop, off64_t off, int whence);
if (_xseek64(iop, (off64_t)0, SEEK_END) < (off64_t)0) {
(void) _xseek64(iop, -iop->_cnt, SEEK_CUR);
p = _xseek64(iop, offset, ptrname);
tres = _xseek64(iop, 0, SEEK_CUR);
(void) _xseek64(iop, 0, SEEK_SET);