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// 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.emplace_back(0, crc32c_t{1});
}
}
} // namespace crc_internal
ABSL_NAMESPACE_END
} // namespace absl
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