Export of internal Abseil changes

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77e710b0ced5792a328e88bcb938a41484bf4cdc by Saleem Abdulrasool <abdulras@google.com>:

absl: add an implementation for UnscaledCycleClock on RISCV

Add an implementation for UnscaledCycleClock on RISC-V targets.

PiperOrigin-RevId: 395982312

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84430fce6760c488ca36401cd530f44268ac710d by Martijn Vels <mvels@google.com>:

Harden CordRepBtreeReader against reading up to or beyond EOF

This change hardens the reader to Next() calls on EOF situations. It changes the 'consumed()' property inside CordRepBtreeReader into a 'remaining()' property which is easier to understand and use than the 'consumed()' property QED the function documentation and use in cord.cc

This change also adds the CharIterator test to the CordTest fixture enabling them to be run with btree cords.

PiperOrigin-RevId: 395971732

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6557e628f2613169da8f693189223acb30e07833 by Martijn Vels <mvels@google.com>:

Add AdvanceAndRead() test addressing the edge case surfaced in b/197776822

This adds a test explicitly exercising all possible AdvanceAndRead() calls on CharIterator. As per the linked bug, a partial or full small read ending exactly at the end of the last edge of a btree cord results in an attempt to read beyond that last edge and subsequent failure. We will fix the bug and enable these tests for btree in a subsequent change.

PiperOrigin-RevId: 395958317
GitOrigin-RevId: 77e710b0ced5792a328e88bcb938a41484bf4cdc
Change-Id: Ie6e21ce36980515165af7cf046cf199ecbe0ddb0

1 files changed, 38 insertions, 3 deletions

diff --git a/absl/strings/cord_test.cc b/absl/strings/cord_test.cc
index 06a7bd6c..50079b7c 100644
--- a/absl/strings/cord_test.cc
+++ b/absl/strings/cord_test.cc
@@ -1591,7 +1591,7 @@ TEST_P(CordTest, CordChunkIteratorOperations) {
   VerifyChunkIterator(subcords, 128);
 }
 
-TEST(CordCharIterator, Traits) {
+TEST_P(CordTest, CharIteratorTraits) {
   static_assert(std::is_copy_constructible<absl::Cord::CharIterator>::value,
                 "");
   static_assert(std::is_copy_assignable<absl::Cord::CharIterator>::value, "");
@@ -1700,7 +1700,7 @@ static void VerifyCharIterator(const absl::Cord& cord) {
   }
 }
 
-TEST(CordCharIterator, Operations) {
+TEST_P(CordTest, CharIteratorOperations) {
   absl::Cord empty_cord;
   VerifyCharIterator(empty_cord);
 
@@ -1729,6 +1729,41 @@ TEST(CordCharIterator, Operations) {
   VerifyCharIterator(subcords);
 }
 
+TEST_P(CordTest, CharIteratorAdvanceAndRead) {
+  // Create a Cord holding 6 flats of 2500 bytes each, and then iterate over it
+  // reading 150, 1500, 2500 and 3000 bytes. This will result in all possible
+  // partial, full and straddled read combinations including reads below
+  // kMaxBytesToCopy. b/197776822 surfaced a bug for a specific partial, small
+  // read 'at end' on Cord which caused a failure on attempting to read past the
+  // end in CordRepBtreeReader which was not covered by any existing test.
+  constexpr int kBlocks = 6;
+  constexpr size_t kBlockSize = 2500;
+  constexpr size_t kChunkSize1 = 1500;
+  constexpr size_t kChunkSize2 = 2500;
+  constexpr size_t kChunkSize3 = 3000;
+  constexpr size_t kChunkSize4 = 150;
+  RandomEngine rng;
+  std::string data = RandomLowercaseString(&rng, kBlocks * kBlockSize);
+  absl::Cord cord;
+  for (int i = 0; i < kBlocks; ++i) {
+    const std::string block = data.substr(i * kBlockSize, kBlockSize);
+    cord.Append(absl::Cord(block));
+  }
+
+  for (size_t chunk_size :
+       {kChunkSize1, kChunkSize2, kChunkSize3, kChunkSize4}) {
+    absl::Cord::CharIterator it = cord.char_begin();
+    size_t offset = 0;
+    while (offset < data.length()) {
+      const size_t n = std::min<size_t>(data.length() - offset, chunk_size);
+      absl::Cord chunk = cord.AdvanceAndRead(&it, n);
+      ASSERT_EQ(chunk.size(), n);
+      ASSERT_EQ(chunk.Compare(data.substr(offset, n)), 0);
+      offset += n;
+    }
+  }
+}
+
 TEST_P(CordTest, StreamingOutput) {
   absl::Cord c =
       absl::MakeFragmentedCord({"A ", "small ", "fragmented ", "Cord", "."});
@@ -1778,7 +1813,7 @@ TEST_P(CordTest, Format) {
   EXPECT_EQ(c, "There were 0003 little pigs.And 1   bad wolf!");
 }
 
-TEST(CordDeathTest, Hardening) {
+TEST_P(CordTest, Hardening) {
   absl::Cord cord("hello");
   // These statement should abort the program in all builds modes.
   EXPECT_DEATH_IF_SUPPORTED(cord.RemovePrefix(6), "");