[committed] libstdc++: Fix test that fails randomly [PR101866]

[Jonathan Wakely]

This test assumes that the same sequence of three values cannot occur,
which is incorect. It's unlikely, but not impossible.

Perform the check in a loop, so that in the unlikely event of an
identical sequence, we retry. If the library code is buggy it will keep
producing the same sequence and the test will time out. If the code is
working correctly then we will usually break out of the loop after one
iteration, or very rarely after two or three.

libstdc++-v3/ChangeLog:

	PR libstdc++/101866
	* testsuite/experimental/random/randint.cc: Loop and retry if
	reseed() produces the same sequence.

Tested x86_64-linux. Committed to trunk. I'll backport too.

-------------- next part --------------
commit 93f1dbc7cdcc4b31ea4061efb4c2acf2d4f81eb8
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Aug 11 22:11:19 2021

    libstdc++: Fix test that fails randomly [PR101866]
    
    This test assumes that the same sequence of three values cannot occur,
    which is incorect. It's unlikely, but not impossible.
    
    Perform the check in a loop, so that in the unlikely event of an
    identical sequence, we retry. If the library code is buggy it will keep
    producing the same sequence and the test will time out. If the code is
    working correctly then we will usually break out of the loop after one
    iteration, or very rarely after two or three.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/101866
            * testsuite/experimental/random/randint.cc: Loop and retry if
            reseed() produces the same sequence.

diff --git a/libstdc++-v3/testsuite/experimental/random/randint.cc b/libstdc++-v3/testsuite/experimental/random/randint.cc
index d6225eba1df..e05151e5ea0 100644
--- a/libstdc++-v3/testsuite/experimental/random/randint.cc
+++ b/libstdc++-v3/testsuite/experimental/random/randint.cc
@@ -34,7 +34,7 @@ test01()
   }
 
   std::experimental::reseed(99u);
-  const long n1[] = {
+  const int n1[] = {
     std::experimental::randint(0, 100),
     std::experimental::randint(0, 100),
     std::experimental::randint(0, 100),
@@ -42,7 +42,7 @@ test01()
     std::experimental::randint(0, 100)
   };
   std::experimental::reseed(99u);
-  const long n2[] = {
+  const int n2[] = {
     std::experimental::randint(0, 100),
     std::experimental::randint(0, 100),
     std::experimental::randint(0, 100),
@@ -52,13 +52,13 @@ test01()
   for (int i = 0; i < 5; ++i)
     VERIFY( n1[i] == n2[i] );
 
-  std::experimental::reseed();
-  const long n3[] = {
-    std::experimental::randint(0, 100),
-    std::experimental::randint(0, 100),
-    std::experimental::randint(0, 100)
-  };
-  VERIFY( !(n3[0] == n1[0] && n3[1] == n1[1] && n3[2] == n1[2]) );
+  do
+  {
+    std::experimental::reseed();
+  }
+  while (std::experimental::randint(0, 100) == n1[0]
+      && std::experimental::randint(0, 100) == n1[1]
+      && std::experimental::randint(0, 100) == n1[2]);
 }
 
 void