100 lines
3.3 KiB
C++
100 lines
3.3 KiB
C++
// Copyright 2022 The Abseil Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "absl/crc/crc32c.h"
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#include <cstdint>
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#include "absl/crc/internal/crc.h"
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#include "absl/crc/internal/crc32c.h"
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#include "absl/crc/internal/crc_memcpy.h"
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#include "absl/strings/string_view.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace {
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const crc_internal::CRC* CrcEngine() {
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static const crc_internal::CRC* engine = crc_internal::CRC::Crc32c();
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return engine;
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}
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constexpr uint32_t kCRC32Xor = 0xffffffffU;
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} // namespace
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namespace crc_internal {
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crc32c_t UnextendCrc32cByZeroes(crc32c_t initial_crc, size_t length) {
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uint32_t crc = static_cast<uint32_t>(initial_crc) ^ kCRC32Xor;
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CrcEngine()->UnextendByZeroes(&crc, length);
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return static_cast<crc32c_t>(crc ^ kCRC32Xor);
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}
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// Called by `absl::ExtendCrc32c()` on strings with size > 64 or when hardware
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// CRC32C support is missing.
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crc32c_t ExtendCrc32cInternal(crc32c_t initial_crc,
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absl::string_view buf_to_add) {
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uint32_t crc = static_cast<uint32_t>(initial_crc) ^ kCRC32Xor;
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CrcEngine()->Extend(&crc, buf_to_add.data(), buf_to_add.size());
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return static_cast<crc32c_t>(crc ^ kCRC32Xor);
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}
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} // namespace crc_internal
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crc32c_t ComputeCrc32c(absl::string_view buf) {
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return ExtendCrc32c(crc32c_t{0}, buf);
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}
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crc32c_t ExtendCrc32cByZeroes(crc32c_t initial_crc, size_t length) {
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uint32_t crc = static_cast<uint32_t>(initial_crc) ^ kCRC32Xor;
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CrcEngine()->ExtendByZeroes(&crc, length);
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return static_cast<crc32c_t>(crc ^ kCRC32Xor);
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}
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crc32c_t ConcatCrc32c(crc32c_t lhs_crc, crc32c_t rhs_crc, size_t rhs_len) {
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uint32_t result = static_cast<uint32_t>(lhs_crc);
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CrcEngine()->ExtendByZeroes(&result, rhs_len);
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return crc32c_t{result ^ static_cast<uint32_t>(rhs_crc)};
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}
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crc32c_t RemoveCrc32cPrefix(crc32c_t crc_a, crc32c_t crc_ab, size_t length_b) {
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return ConcatCrc32c(crc_a, crc_ab, length_b);
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}
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crc32c_t MemcpyCrc32c(void* dest, const void* src, size_t count,
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crc32c_t initial_crc) {
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return static_cast<crc32c_t>(
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crc_internal::Crc32CAndCopy(dest, src, count, initial_crc, false));
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}
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// Remove a Suffix of given size from a buffer
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//
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// Given a CRC32C of an existing buffer, `full_string_crc`; the CRC32C of a
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// suffix of that buffer to remove, `suffix_crc`; and suffix buffer's length,
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// `suffix_len` return the CRC32C of the buffer with suffix removed
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//
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// This operation has a runtime cost of O(log(`suffix_len`))
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crc32c_t RemoveCrc32cSuffix(crc32c_t full_string_crc, crc32c_t suffix_crc,
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size_t suffix_len) {
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uint32_t result = static_cast<uint32_t>(full_string_crc) ^
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static_cast<uint32_t>(suffix_crc);
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CrcEngine()->UnextendByZeroes(&result, suffix_len);
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return crc32c_t{result};
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}
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ABSL_NAMESPACE_END
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} // namespace absl
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