[Bug libstdc++/63332] problem with VERIFY in ext/random/k_distribution/operators/serialize.cc execution test

["richard at netbsd dot org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63332

--- Comment #5 from Richard PALO <richard at netbsd dot org> ---
By the way, in gdb, here are the complete u and v variables after
serialisation:

gdb) p u
$1 = {_M_param = {_M_lambda = 2, _M_mu = 1.5, _M_nu = 3}, _M_gd1 = {
    _M_param = {_M_alpha = 2, _M_beta = 0.5, _M_malpha = 2, 
      _M_a2 = 0.25819888974716108}, _M_nd = {_M_param = {_M_mean = 0, 
        _M_stddev = 1}, _M_saved = -1.0868180442613568, 
      _M_saved_available = true}}, _M_gd2 = {_M_param = {_M_alpha = 3, 
      _M_beta = 0.5, _M_malpha = 3, _M_a2 = 0.20412414523193152}, _M_nd = {
      _M_param = {_M_mean = 0, _M_stddev = 1}, _M_saved = 0.18913187340436784, 
      _M_saved_available = true}}}
(gdb) p v
$2 = {_M_param = {_M_lambda = 2, _M_mu = 1.5, _M_nu = 3}, _M_gd1 = {
    _M_param = {_M_alpha = 2, _M_beta = 0.5, _M_malpha = 2, 
      _M_a2 = 0.25819888974716108}, _M_nd = {_M_param = {_M_mean = 0, 
        _M_stddev = 1}, _M_saved = -1.0868180442613568, 
      _M_saved_available = true}}, _M_gd2 = {_M_param = {_M_alpha = 3, 
      _M_beta = 0.5, _M_malpha = 3, _M_a2 = 0.20412414523193152}, _M_nd = {
      _M_param = {_M_mean = 0, _M_stddev = 1}, _M_saved = 0.1891318734043678, 
      _M_saved_available = true}}}

I notice _M_saved in v is truncated by 1 (the trailing '4')...
that is, 16 and not 17 digits after the decimal are copied.