Abseil Common Libraries (C++) (grcp 依赖)
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100 lines
3.3 KiB
100 lines
3.3 KiB
// 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(ToCrc32c(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 static_cast<crc32c_t>(result) ^ 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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crc32c_t crc_with_suffix_zeroed = |
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suffix_crc ^ full_string_crc ^ |
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ExtendCrc32cByZeroes(ToCrc32c(0), suffix_len); |
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return crc_internal::UnextendCrc32cByZeroes( |
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crc_with_suffix_zeroed, suffix_len); |
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} |
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ABSL_NAMESPACE_END |
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} // namespace absl
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