skip Cholesky decomposition in is>>n_mv_dist

normal_mv_distribution maintains the variance-covariance matrix param
in Cholesky-decomposed form.  Existing param_type constructors, when
taking a full or lower-triangle varcov matrix, perform Cholesky
decomposition to convert it to the internal representation.  This
internal representation is visible both in the varcov() result, and in
the streamed-out representation of a normal_mv_distribution object.

The problem is that when that representation is streamed back in, the
read-back decomposed varcov matrix is used as a lower-triangle
non-decomposed varcov matrix, and it undergoes Cholesky decomposition
again.  So, each cycle of stream-out/stream-in changes the varcov
matrix to its "square root", instead of restoring the original
params.

This patch includes Corentin's changes that introduce verification in
testsuite/ext/random/normal_mv_distribution/operators/serialize.cc and
other similar tests that the object read back in compares equal to the
written-out object: the modified tests pass only if (u == v).

This patch also fixes the error exposed by his change, introducing an
alternate private constructor for param_type, used only by operator>>.


for  libstdc++-v3/ChangeLog

	* include/ext/random
	(normal_mv_distribution::param_type::param_type): New private
	ctor taking a decomposed varcov matrix, for use by...
	(operator>>): ... this, befriended.
	* include/ext/random.tcc (operator>>): Use it.
	(normal_mv_distribution::param_type::_M_init_lower): Adjust
	member function name in exception message.

for  libstdc++-v3/ChangeLog
from  Corentin Gay  <gay@adacore.com>

	* testsuite/ext/random/beta_distribution/operators/serialize.cc,
	testsuite/ext/random/hypergeometric_distribution/operators/serialize.cc,
	testsuite/ext/random/normal_mv_distribution/operators/serialize.cc,
	testsuite/ext/random/triangular_distribution/operators/serialize.cc,
	testsuite/ext/random/von_mises_distribution/operators/serialize.cc:
	Add call to `VERIFY`.

From-SVN: r274233

libstdc++-v3/ChangeLog

@@ -1,3 +1,22 @@
+2019-08-09  Corentin Gay  <gay@adacore.com>
+
+	* testsuite/ext/random/beta_distribution/operators/serialize.cc,
+	testsuite/ext/random/hypergeometric_distribution/operators/serialize.cc,
+	testsuite/ext/random/normal_mv_distribution/operators/serialize.cc,
+	testsuite/ext/random/triangular_distribution/operators/serialize.cc,
+	testsuite/ext/random/von_mises_distribution/operators/serialize.cc:
+	Add call to `VERIFY`.
+
+2019-08-09  Alexandre Oliva <oliva@adacore.com>
+
+	* include/ext/random
+	(normal_mv_distribution::param_type::param_type): New private
+	ctor taking a decomposed varcov matrix, for use by...
+	(operator>>): ... this, befriended.
+	* include/ext/random.tcc (operator>>): Use it.
+	(normal_mv_distribution::param_type::_M_init_lower): Adjust
+	member function name in exception message.
+
 2019-08-08  Jonathan Wakely  <jwakely@redhat.com>
 
 	P0325R4 to_array from LFTS with updates

libstdc++-v3/include/ext/random

@@ -752,6 +752,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 				_InputIterator2 __varbegin,
 				_InputIterator2 __varend);
 
+	// param_type constructors apply Cholesky decomposition to the
+	// varcov matrix in _M_init_full and _M_init_lower, but the
+	// varcov matrix output ot a stream is already decomposed, so
+	// we need means to restore it as-is when reading it back in.
+	template<size_t _Dimen1, typename _RealType1,
+		 typename _CharT, typename _Traits>
+	friend std::basic_istream<_CharT, _Traits>&
+	operator>>(std::basic_istream<_CharT, _Traits>& __is,
+		   __gnu_cxx::normal_mv_distribution<_Dimen1, _RealType1>&
+		   __x);
+	param_type(std::array<_RealType, _Dimen> const &__mean,
+		   std::array<_RealType, _M_t_size> const &__varcov)
+	  : _M_mean (__mean), _M_t (__varcov)
+	{}
+
 	std::array<_RealType, _Dimen> _M_mean;
 	std::array<_RealType, _M_t_size> _M_t;
       };

libstdc++-v3/include/ext/random.tcc

@@ -581,7 +581,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	    __sum = *__varcovbegin++ - __sum;
 	    if (__builtin_expect(__sum <= _RealType(0), 0))
 	      std::__throw_runtime_error(__N("normal_mv_distribution::"
-					     "param_type::_M_init_full"));
+					     "param_type::_M_init_lower"));
 	    *__w++ = std::sqrt(__sum);
 	  }
       }
@@ -709,9 +709,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       __is >> __x._M_nd;
 
+      // The param_type temporary is built with a private constructor,
+      // to skip the Cholesky decomposition that would be performed
+      // otherwise.
       __x.param(typename normal_mv_distribution<_Dimen, _RealType>::
-		param_type(__mean.begin(), __mean.end(),
-			   __varcov.begin(), __varcov.end()));
+		param_type(__mean, __varcov));
 
       __is.flags(__flags);
       return __is;

libstdc++-v3/testsuite/ext/random/beta_distribution/operators/serialize.cc

@@ -23,6 +23,7 @@
 
 #include <ext/random>
 #include <sstream>
+#include <testsuite_hooks.h>
 
 void
 test01()
@@ -35,6 +36,7 @@ test01()
   str << u;
 
   str >> v;
+  VERIFY( u == v );
 }
 
 int main()

libstdc++-v3/testsuite/ext/random/hypergeometric_distribution/operators/serialize.cc

@@ -38,6 +38,7 @@ test01()
   str << u;
 
   str >> v;
+  VERIFY( u == v );
 }
 
 int

libstdc++-v3/testsuite/ext/random/normal_mv_distribution/operators/serialize.cc

@@ -23,6 +23,7 @@
 
 #include <ext/random>
 #include <sstream>
+#include <testsuite_hooks.h>
 
 void
 test01()
@@ -35,6 +36,7 @@ test01()
   str << u;
 
   str >> v;
+  VERIFY( u == v );
 }
 
 int main()

libstdc++-v3/testsuite/ext/random/triangular_distribution/operators/serialize.cc

@@ -23,6 +23,7 @@
 
 #include <ext/random>
 #include <sstream>
+#include <testsuite_hooks.h>
 
 void
 test01()
@@ -35,6 +36,7 @@ test01()
   str << u;
 
   str >> v;
+  VERIFY( u == v );
 }
 
 int main()

libstdc++-v3/testsuite/ext/random/von_mises_distribution/operators/serialize.cc

@@ -23,6 +23,7 @@
 
 #include <ext/random>
 #include <sstream>
+#include <testsuite_hooks.h>
 
 void
 test01()
@@ -35,6 +36,7 @@ test01()
   str << u;
 
   str >> v;
+  VERIFY( u == v );
 }
 
 int main()