crc32c.cc (3266B)
1 // Copyright 2022 The Abseil Authors 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // https://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 #include "absl/crc/crc32c.h" 16 17 #include <cstdint> 18 19 #include "absl/crc/internal/crc.h" 20 #include "absl/crc/internal/crc32c.h" 21 #include "absl/crc/internal/crc_memcpy.h" 22 #include "absl/strings/string_view.h" 23 24 namespace absl { 25 ABSL_NAMESPACE_BEGIN 26 27 namespace { 28 29 const crc_internal::CRC* CrcEngine() { 30 static const crc_internal::CRC* engine = crc_internal::CRC::Crc32c(); 31 return engine; 32 } 33 34 constexpr uint32_t kCRC32Xor = 0xffffffffU; 35 36 } // namespace 37 38 namespace crc_internal { 39 40 crc32c_t UnextendCrc32cByZeroes(crc32c_t initial_crc, size_t length) { 41 uint32_t crc = static_cast<uint32_t>(initial_crc) ^ kCRC32Xor; 42 CrcEngine()->UnextendByZeroes(&crc, length); 43 return static_cast<crc32c_t>(crc ^ kCRC32Xor); 44 } 45 46 // Called by `absl::ExtendCrc32c()` on strings with size > 64 or when hardware 47 // CRC32C support is missing. 48 crc32c_t ExtendCrc32cInternal(crc32c_t initial_crc, 49 absl::string_view buf_to_add) { 50 uint32_t crc = static_cast<uint32_t>(initial_crc) ^ kCRC32Xor; 51 CrcEngine()->Extend(&crc, buf_to_add.data(), buf_to_add.size()); 52 return static_cast<crc32c_t>(crc ^ kCRC32Xor); 53 } 54 55 } // namespace crc_internal 56 57 crc32c_t ExtendCrc32cByZeroes(crc32c_t initial_crc, size_t length) { 58 uint32_t crc = static_cast<uint32_t>(initial_crc) ^ kCRC32Xor; 59 CrcEngine()->ExtendByZeroes(&crc, length); 60 return static_cast<crc32c_t>(crc ^ kCRC32Xor); 61 } 62 63 crc32c_t ConcatCrc32c(crc32c_t lhs_crc, crc32c_t rhs_crc, size_t rhs_len) { 64 uint32_t result = static_cast<uint32_t>(lhs_crc); 65 CrcEngine()->ExtendByZeroes(&result, rhs_len); 66 return crc32c_t{result ^ static_cast<uint32_t>(rhs_crc)}; 67 } 68 69 crc32c_t RemoveCrc32cPrefix(crc32c_t crc_a, crc32c_t crc_ab, size_t length_b) { 70 return ConcatCrc32c(crc_a, crc_ab, length_b); 71 } 72 73 crc32c_t MemcpyCrc32c(void* dest, const void* src, size_t count, 74 crc32c_t initial_crc) { 75 return static_cast<crc32c_t>( 76 crc_internal::Crc32CAndCopy(dest, src, count, initial_crc, false)); 77 } 78 79 // Remove a Suffix of given size from a buffer 80 // 81 // Given a CRC32C of an existing buffer, `full_string_crc`; the CRC32C of a 82 // suffix of that buffer to remove, `suffix_crc`; and suffix buffer's length, 83 // `suffix_len` return the CRC32C of the buffer with suffix removed 84 // 85 // This operation has a runtime cost of O(log(`suffix_len`)) 86 crc32c_t RemoveCrc32cSuffix(crc32c_t full_string_crc, crc32c_t suffix_crc, 87 size_t suffix_len) { 88 uint32_t result = static_cast<uint32_t>(full_string_crc) ^ 89 static_cast<uint32_t>(suffix_crc); 90 CrcEngine()->UnextendByZeroes(&result, suffix_len); 91 return crc32c_t{result}; 92 } 93 94 ABSL_NAMESPACE_END 95 } // namespace absl