Fix a corner case in SpyHashState for exact boundaries.

AbslHash allows for piecewise chunks to be streamed incrementally into hash states and requires them to hash identically to one giant stream.  The exact size window for this is an internal details `PiecewiseChunkSize`.  There was an off by one error in this code.  Add tests and fix it.

PiperOrigin-RevId: 602463183
Change-Id: I159bbb5e7e745f55b2fe6eaf0d2735bd0a08aca9

1 files changed, 21 insertions, 0 deletions

diff --git a/absl/strings/cord_test.cc b/absl/strings/cord_test.cc
index f1a5f39c..69b1a69e 100644
--- a/absl/strings/cord_test.cc
+++ b/absl/strings/cord_test.cc
@@ -42,6 +42,7 @@
 #include "absl/container/fixed_array.h"
 #include "absl/functional/function_ref.h"
 #include "absl/hash/hash.h"
+#include "absl/hash/hash_testing.h"
 #include "absl/log/check.h"
 #include "absl/log/log.h"
 #include "absl/random/random.h"
@@ -2013,6 +2014,26 @@ TEST(CordTest, CordMemoryUsageBTree) {
                 rep2_size);
 }
 
+TEST(CordTest, TestHashFragmentation) {
+  // Make sure we hit these boundary cases precisely.
+  EXPECT_EQ(1024, absl::hash_internal::PiecewiseChunkSize());
+  EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly({
+      absl::Cord(),
+      absl::MakeFragmentedCord({std::string(600, 'a'), std::string(600, 'a')}),
+      absl::MakeFragmentedCord({std::string(1200, 'a')}),
+      absl::MakeFragmentedCord({std::string(900, 'b'), std::string(900, 'b')}),
+      absl::MakeFragmentedCord({std::string(1800, 'b')}),
+      absl::MakeFragmentedCord(
+          {std::string(2000, 'c'), std::string(2000, 'c')}),
+      absl::MakeFragmentedCord({std::string(4000, 'c')}),
+      absl::MakeFragmentedCord({std::string(1024, 'd')}),
+      absl::MakeFragmentedCord({std::string(1023, 'd'), "d"}),
+      absl::MakeFragmentedCord({std::string(1025, 'e')}),
+      absl::MakeFragmentedCord({std::string(1024, 'e'), "e"}),
+      absl::MakeFragmentedCord({std::string(1023, 'e'), "e", "e"}),
+  }));
+}
+
 // Regtest for a change that had to be rolled back because it expanded out
 // of the InlineRep too soon, which was observable through MemoryUsage().
 TEST_P(CordTest, CordMemoryUsageInlineRep) {