[gcc r11-9970] libstdc++: Fix deserialization for std::normal_distribution [PR105502]

[Jonathan Wakely]

https://gcc.gnu.org/g:eb049ef0f4651786aa49110189487e7f8bf343a6

commit r11-9970-geb049ef0f4651786aa49110189487e7f8bf343a6
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri May 6 21:19:17 2022 +0100

    libstdc++: Fix deserialization for std::normal_distribution [PR105502]
    
    This fixes a regression in std::normal_distribution deserialization that
    caused the object to be left unchanged if the __state_avail value read
    from the stream was false.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/105502
            * include/bits/random.tcc
            (operator>>(basic_istream<C,T>&, normal_distribution<R>&)):
            Update state when __state_avail is false.
            * testsuite/26_numerics/random/normal_distribution/operators/serialize.cc:
            Check that deserialized object equals serialized one.
    
    (cherry picked from commit 909ef4e2727ddc50a32d6ad379a1f1ccc1043c6a)

Diff:
---
 libstdc++-v3/include/bits/random.tcc               |  2 +-
 .../normal_distribution/operators/serialize.cc     | 36 +++++++++++++++++++++-
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/bits/random.tcc b/libstdc++-v3/include/bits/random.tcc
index 22ae1f38ebb..2898f7f17e6 100644
--- a/libstdc++-v3/include/bits/random.tcc
+++ b/libstdc++-v3/include/bits/random.tcc
@@ -1955,7 +1955,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       bool __saved_avail;
       if (__is >> __mean >> __stddev >> __saved_avail)
 	{
-	  if (__saved_avail && (__is >> __x._M_saved))
+	  if (!__saved_avail || (__is >> __x._M_saved))
 	    {
 	      __x._M_saved_available = __saved_avail;
 	      __x.param(param_type(__mean, __stddev));
diff --git a/libstdc++-v3/testsuite/26_numerics/random/normal_distribution/operators/serialize.cc b/libstdc++-v3/testsuite/26_numerics/random/normal_distribution/operators/serialize.cc
index f947f8ae848..e8705ca7879 100644
--- a/libstdc++-v3/testsuite/26_numerics/random/normal_distribution/operators/serialize.cc
+++ b/libstdc++-v3/testsuite/26_numerics/random/normal_distribution/operators/serialize.cc
@@ -25,6 +25,7 @@
 
 #include <random>
 #include <sstream>
+#include <testsuite_hooks.h>
 
 void
 test01()
@@ -37,10 +38,43 @@ test01()
   str << u;
 
   str >> v;
+  VERIFY( u == v );
+}
+
+void
+test_pr105502()
+{
+  // PR libstdc++/105502 std::normal_distribution deserialization issue
+  std::stringstream str;
+  std::normal_distribution<> d{1, 2}, d2;
+  std::minstd_rand0 g;
+  str << d;
+  VERIFY( str );
+  str >> d2;
+  VERIFY( str );
+  VERIFY( d == d2 );
+
+  (void) d(g); // sets d._M_saved_available = true
+  str.str("");
+  str.clear();
+  str << d;
+  VERIFY( str );
+  str >> d2;
+  VERIFY( str );
+  VERIFY( d == d2 );
+
+  (void) d(g); // sets d._M_saved_available = false
+  str.str("");
+  str.clear();
+  str << d;
+  VERIFY( str );
+  str >> d2;
+  VERIFY( str );
+  VERIFY( d == d2 );
 }
 
 int main()
 {
   test01();
-  return 0;
+  test_pr105502();
 }