Merge bitcoin/bitcoin#29012: fuzz: Avoid timeout in bitdeque

fad1903b8a85506378101c1f857ba47b4a058fb4 fuzz: Avoid timeout in bitdeque (MarcoFalke)

Pull request description:

  Avoid timeouts such as https://github.com/bitcoin/bitcoin/issues/28812#issuecomment-1842914664

  This is done by:

  * Limiting the maximum number of iterations if the maximum size of the container is "large" (see the magic numbers in the code).
  * Check the equality only once. This should be fine, because if a crash were to happen in the equality check, but the crash doesn't happen if further iterations were run, the fuzz engine should eventually find the crash by truncating the fuzz input.

ACKs for top commit:
  sipa:
    utACK fad1903b8a85506378101c1f857ba47b4a058fb4
  dergoegge:
    utACK fad1903b8a85506378101c1f857ba47b4a058fb4
  brunoerg:
    crACK fad1903b8a85506378101c1f857ba47b4a058fb4

Tree-SHA512: d3d83acb3e736b8fcaf5d17ce225ac82a9f9a2efea048512d2fed594ba6c76c25bae72eb0fab3276d4db37baec0752e5367cecfb18161301b921fed09693045e

1 files changed, 16 insertions, 16 deletions

diff --git a/src/test/fuzz/bitdeque.cpp b/src/test/fuzz/bitdeque.cpp
index 65f5cb3fd0..d5cc9cfd34 100644
--- a/src/test/fuzz/bitdeque.cpp
+++ b/src/test/fuzz/bitdeque.cpp
@@ -53,21 +53,11 @@ FUZZ_TARGET(bitdeque, .init = InitRandData)
         --initlen;
     }
 
-    LIMITED_WHILE(provider.remaining_bytes() > 0, 900)
+    const auto iter_limit{maxlen > 6000 ? 90U : 900U};
+    LIMITED_WHILE(provider.remaining_bytes() > 0, iter_limit)
     {
-        {
-            assert(deq.size() == bitdeq.size());
-            auto it = deq.begin();
-            auto bitit = bitdeq.begin();
-            auto itend = deq.end();
-            while (it != itend) {
-                assert(*it == *bitit);
-                ++it;
-                ++bitit;
-            }
-        }
-
-        CallOneOf(provider,
+        CallOneOf(
+            provider,
             [&] {
                 // constructor()
                 deq = std::deque<bool>{};
@@ -535,7 +525,17 @@ FUZZ_TARGET(bitdeque, .init = InitRandData)
                     assert(it == deq.begin() + before);
                     assert(bitit == bitdeq.begin() + before);
                 }
-            }
-        );
+            });
+    }
+    {
+        assert(deq.size() == bitdeq.size());
+        auto it = deq.begin();
+        auto bitit = bitdeq.begin();
+        auto itend = deq.end();
+        while (it != itend) {
+            assert(*it == *bitit);
+            ++it;
+            ++bitit;
+        }
     }
 }