/usr/include/ITK-4.5/eispack/epslon.h is in libinsighttoolkit4-dev 4.5.0-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | extern v3p_netlib_doublereal v3p_netlib_epslon_(
v3p_netlib_doublereal *x
);
|