Find Microsoft .NET Framework versions.

        Parameters
        ----------
        bits: int
            Platform number of bits: 32 or 64.

def _find_dot_net_versions(self, bits):
        """
        Find Microsoft .NET Framework versions.

        Parameters
        ----------
        bits: int
            Platform number of bits: 32 or 64.
        """
        # Find actual .NET version in registry
        reg_ver = self.ri.lookup(self.ri.vc, 'frameworkver%d' % bits)
        dot_net_dir = getattr(self, 'FrameworkDir%d' % bits)
        ver = reg_ver or self._use_last_dir_name(dot_net_dir, 'v') or ''

        # Set .NET versions for specified MSVC++ version
        if self.vc_ver >= 12.0:
            frameworkver = (ver, 'v4.0')
        elif self.vc_ver >= 10.0:
            frameworkver = ('v4.0.30319' if ver.lower()[:2] != 'v4' else ver,
                            'v3.5')
        elif self.vc_ver == 9.0:
            frameworkver = ('v3.5', 'v2.0.50727')
        if self.vc_ver == 8.0:
            frameworkver = ('v3.0', 'v2.0.50727')
        return frameworkver