1 files changed, 130 insertions, 0 deletions
diff --git a/absl/crc/internal/crc_cord_state.cc b/absl/crc/internal/crc_cord_state.cc
new file mode 100644
index 00000000..d0be0ddd
--- /dev/null
+++ b/absl/crc/internal/crc_cord_state.cc
@@ -0,0 +1,130 @@
+// Copyright 2022 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/crc/internal/crc_cord_state.h"
+
+#include <cassert>
+
+#include "absl/base/config.h"
+#include "absl/numeric/bits.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace crc_internal {
+
+CrcCordState::RefcountedRep* CrcCordState::RefSharedEmptyRep() {
+  static CrcCordState::RefcountedRep* empty = new CrcCordState::RefcountedRep;
+
+  assert(empty->count.load(std::memory_order_relaxed) >= 1);
+  assert(empty->rep.removed_prefix.length == 0);
+  assert(empty->rep.prefix_crc.empty());
+
+  Ref(empty);
+  return empty;
+}
+
+CrcCordState::CrcCordState() : refcounted_rep_(new RefcountedRep) {}
+
+CrcCordState::CrcCordState(const CrcCordState& other)
+    : refcounted_rep_(other.refcounted_rep_) {
+  Ref(refcounted_rep_);
+}
+
+CrcCordState::CrcCordState(CrcCordState&& other)
+    : refcounted_rep_(other.refcounted_rep_) {
+  // Make `other` valid for use after move.
+  other.refcounted_rep_ = RefSharedEmptyRep();
+}
+
+CrcCordState& CrcCordState::operator=(const CrcCordState& other) {
+  if (this != &other) {
+    Unref(refcounted_rep_);
+    refcounted_rep_ = other.refcounted_rep_;
+    Ref(refcounted_rep_);
+  }
+  return *this;
+}
+
+CrcCordState& CrcCordState::operator=(CrcCordState&& other) {
+  if (this != &other) {
+    Unref(refcounted_rep_);
+    refcounted_rep_ = other.refcounted_rep_;
+    // Make `other` valid for use after move.
+    other.refcounted_rep_ = RefSharedEmptyRep();
+  }
+  return *this;
+}
+
+CrcCordState::~CrcCordState() {
+  Unref(refcounted_rep_);
+}
+
+crc32c_t CrcCordState::Checksum() const {
+  if (rep().prefix_crc.empty()) {
+    return absl::crc32c_t{0};
+  }
+  if (IsNormalized()) {
+    return rep().prefix_crc.back().crc;
+  }
+  return absl::RemoveCrc32cPrefix(
+      rep().removed_prefix.crc, rep().prefix_crc.back().crc,
+      rep().prefix_crc.back().length - rep().removed_prefix.length);
+}
+
+CrcCordState::PrefixCrc CrcCordState::NormalizedPrefixCrcAtNthChunk(
+    size_t n) const {
+  assert(n < NumChunks());
+  if (IsNormalized()) {
+    return rep().prefix_crc[n];
+  }
+  size_t length = rep().prefix_crc[n].length - rep().removed_prefix.length;
+  return PrefixCrc(length,
+                   absl::RemoveCrc32cPrefix(rep().removed_prefix.crc,
+                                            rep().prefix_crc[n].crc, length));
+}
+
+void CrcCordState::Normalize() {
+  if (IsNormalized() || rep().prefix_crc.empty()) {
+    return;
+  }
+
+  Rep* r = mutable_rep();
+  for (auto& prefix_crc : r->prefix_crc) {
+    size_t remaining = prefix_crc.length - r->removed_prefix.length;
+    prefix_crc.crc = absl::RemoveCrc32cPrefix(r->removed_prefix.crc,
+                                              prefix_crc.crc, remaining);
+    prefix_crc.length = remaining;
+  }
+  r->removed_prefix = PrefixCrc();
+}
+
+void CrcCordState::Poison() {
+  Rep* rep = mutable_rep();
+  if (NumChunks() > 0) {
+    for (auto& prefix_crc : rep->prefix_crc) {
+      // This is basically CRC32::Scramble().
+      uint32_t crc = static_cast<uint32_t>(prefix_crc.crc);
+      crc += 0x2e76e41b;
+      crc = absl::rotr(crc, 17);
+      prefix_crc.crc = crc32c_t{crc};
+    }
+  } else {
+    // Add a fake corrupt chunk.
+    rep->prefix_crc.push_back(PrefixCrc(0, crc32c_t{1}));
+  }
+}
+
+}  // namespace crc_internal
+ABSL_NAMESPACE_END
+}  // namespace absl