191 lines
7.1 KiB
C++
191 lines
7.1 KiB
C++
// 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.
|
|
//
|
|
// -----------------------------------------------------------------------------
|
|
// File: crc32c.h
|
|
// -----------------------------------------------------------------------------
|
|
//
|
|
// This header file defines the API for computing CRC32C values as checksums
|
|
// for arbitrary sequences of bytes provided as a string buffer.
|
|
//
|
|
// The API includes the basic functions for computing such CRC32C values and
|
|
// some utility functions for performing more efficient mathematical
|
|
// computations using an existing checksum.
|
|
#ifndef ABSL_CRC_CRC32C_H_
|
|
#define ABSL_CRC_CRC32C_H_
|
|
|
|
#include <cstdint>
|
|
#include <ostream>
|
|
|
|
#include "absl/crc/internal/crc32c_inline.h"
|
|
#include "absl/strings/str_format.h"
|
|
#include "absl/strings/string_view.h"
|
|
|
|
namespace absl {
|
|
ABSL_NAMESPACE_BEGIN
|
|
|
|
//-----------------------------------------------------------------------------
|
|
// crc32c_t
|
|
//-----------------------------------------------------------------------------
|
|
|
|
// `crc32c_t` defines a strongly-typed integer for holding a CRC32C value.
|
|
//
|
|
// Some operators are intentionally omitted. Only equality operators are defined
|
|
// so that `crc32c_t` can be directly compared. Methods for putting `crc32c_t`
|
|
// directly into a set are omitted because this is bug-prone due to checksum
|
|
// collisions. Use an explicit conversion to the `uint32_t` space for operations
|
|
// that treat `crc32c_t` as an integer.
|
|
class crc32c_t final {
|
|
public:
|
|
crc32c_t() = default;
|
|
constexpr explicit crc32c_t(uint32_t crc) : crc_(crc) {}
|
|
|
|
crc32c_t(const crc32c_t&) = default;
|
|
crc32c_t& operator=(const crc32c_t&) = default;
|
|
|
|
explicit operator uint32_t() const { return crc_; }
|
|
|
|
friend bool operator==(crc32c_t lhs, crc32c_t rhs) {
|
|
return static_cast<uint32_t>(lhs) == static_cast<uint32_t>(rhs);
|
|
}
|
|
|
|
friend bool operator!=(crc32c_t lhs, crc32c_t rhs) { return !(lhs == rhs); }
|
|
|
|
template <typename Sink>
|
|
friend void AbslStringify(Sink& sink, crc32c_t crc) {
|
|
absl::Format(&sink, "%08x", static_cast<uint32_t>(crc));
|
|
}
|
|
|
|
private:
|
|
uint32_t crc_;
|
|
};
|
|
|
|
|
|
namespace crc_internal {
|
|
// Non-inline code path for `absl::ExtendCrc32c()`. Do not call directly.
|
|
// Call `absl::ExtendCrc32c()` (defined below) instead.
|
|
crc32c_t ExtendCrc32cInternal(crc32c_t initial_crc,
|
|
absl::string_view buf_to_add);
|
|
} // namespace crc_internal
|
|
|
|
// -----------------------------------------------------------------------------
|
|
// CRC32C Computation Functions
|
|
// -----------------------------------------------------------------------------
|
|
|
|
// ComputeCrc32c()
|
|
//
|
|
// Returns the CRC32C value of the provided string.
|
|
crc32c_t ComputeCrc32c(absl::string_view buf);
|
|
|
|
// ExtendCrc32c()
|
|
//
|
|
// Computes a CRC32C value from an `initial_crc` CRC32C value including the
|
|
// `buf_to_add` bytes of an additional buffer. Using this function is more
|
|
// efficient than computing a CRC32C value for the combined buffer from
|
|
// scratch.
|
|
//
|
|
// Note: `ExtendCrc32c` with an initial_crc of 0 is equivalent to
|
|
// `ComputeCrc32c`.
|
|
//
|
|
// This operation has a runtime cost of O(`buf_to_add.size()`)
|
|
inline crc32c_t ExtendCrc32c(crc32c_t initial_crc,
|
|
absl::string_view buf_to_add) {
|
|
// Approximately 75% of calls have size <= 64.
|
|
if (buf_to_add.size() <= 64) {
|
|
uint32_t crc = static_cast<uint32_t>(initial_crc);
|
|
if (crc_internal::ExtendCrc32cInline(&crc, buf_to_add.data(),
|
|
buf_to_add.size())) {
|
|
return crc32c_t{crc};
|
|
}
|
|
}
|
|
return crc_internal::ExtendCrc32cInternal(initial_crc, buf_to_add);
|
|
}
|
|
|
|
// ExtendCrc32cByZeroes()
|
|
//
|
|
// Computes a CRC32C value for a buffer with an `initial_crc` CRC32C value,
|
|
// where `length` bytes with a value of 0 are appended to the buffer. Using this
|
|
// function is more efficient than computing a CRC32C value for the combined
|
|
// buffer from scratch.
|
|
//
|
|
// This operation has a runtime cost of O(log(`length`))
|
|
crc32c_t ExtendCrc32cByZeroes(crc32c_t initial_crc, size_t length);
|
|
|
|
// MemcpyCrc32c()
|
|
//
|
|
// Copies `src` to `dest` using `memcpy()` semantics, returning the CRC32C
|
|
// value of the copied buffer.
|
|
//
|
|
// Using `MemcpyCrc32c()` is potentially faster than performing the `memcpy()`
|
|
// and `ComputeCrc32c()` operations separately.
|
|
crc32c_t MemcpyCrc32c(void* dest, const void* src, size_t count,
|
|
crc32c_t initial_crc = crc32c_t{0});
|
|
|
|
// -----------------------------------------------------------------------------
|
|
// CRC32C Arithmetic Functions
|
|
// -----------------------------------------------------------------------------
|
|
|
|
// The following functions perform arithmetic on CRC32C values, which are
|
|
// generally more efficient than recalculating any given result's CRC32C value.
|
|
|
|
// ConcatCrc32c()
|
|
//
|
|
// Calculates the CRC32C value of two buffers with known CRC32C values
|
|
// concatenated together.
|
|
//
|
|
// Given a buffer with CRC32C value `crc1` and a buffer with
|
|
// CRC32C value `crc2` and length, `crc2_length`, returns the CRC32C value of
|
|
// the concatenation of these two buffers.
|
|
//
|
|
// This operation has a runtime cost of O(log(`crc2_length`)).
|
|
crc32c_t ConcatCrc32c(crc32c_t crc1, crc32c_t crc2, size_t crc2_length);
|
|
|
|
// RemoveCrc32cPrefix()
|
|
//
|
|
// Calculates the CRC32C value of an existing buffer with a series of bytes
|
|
// (the prefix) removed from the beginning of that buffer.
|
|
//
|
|
// Given the CRC32C value of an existing buffer, `full_string_crc`; The CRC32C
|
|
// value of a prefix of that buffer, `prefix_crc`; and the length of the buffer
|
|
// with the prefix removed, `remaining_string_length` , return the CRC32C
|
|
// value of the buffer with the prefix removed.
|
|
//
|
|
// This operation has a runtime cost of O(log(`remaining_string_length`)).
|
|
crc32c_t RemoveCrc32cPrefix(crc32c_t prefix_crc, crc32c_t full_string_crc,
|
|
size_t remaining_string_length);
|
|
// RemoveCrc32cSuffix()
|
|
//
|
|
// Calculates the CRC32C value of an existing buffer with a series of bytes
|
|
// (the suffix) removed from the end of that buffer.
|
|
//
|
|
// Given a CRC32C value of an existing buffer `full_string_crc`, the CRC32C
|
|
// value of the suffix to remove `suffix_crc`, and the length of that suffix
|
|
// `suffix_len`, returns the CRC32C value of the buffer with suffix removed.
|
|
//
|
|
// This operation has a runtime cost of O(log(`suffix_len`))
|
|
crc32c_t RemoveCrc32cSuffix(crc32c_t full_string_crc, crc32c_t suffix_crc,
|
|
size_t suffix_length);
|
|
|
|
// operator<<
|
|
//
|
|
// Streams the CRC32C value `crc` to the stream `os`.
|
|
inline std::ostream& operator<<(std::ostream& os, crc32c_t crc) {
|
|
return os << absl::StreamFormat("%08x", static_cast<uint32_t>(crc));
|
|
}
|
|
|
|
ABSL_NAMESPACE_END
|
|
} // namespace absl
|
|
|
|
#endif // ABSL_CRC_CRC32C_H_
|