// 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/crc32c.h"

#include <cstdint>

#include "absl/crc/internal/crc.h"

#include "absl/crc/internal/crc32c.h"

#include "absl/crc/internal/crc_memcpy.h"

#include "absl/strings/string_view.h"

namespace absl {

ABSL_NAMESPACE_BEGIN

namespace {

const crc_internal::CRC* CrcEngine() {

  static const crc_internal::CRC* engine = crc_internal::CRC::Crc32c();

  return engine;

}

constexpr uint32_t kCRC32Xor = 0xffffffffU;

}  // namespace

namespace crc_internal {

crc32c_t UnextendCrc32cByZeroes(crc32c_t initial_crc, size_t length) {

  uint32_t crc = static_cast<uint32_t>(initial_crc) ^ kCRC32Xor;

  CrcEngine()->UnextendByZeroes(&crc, length);

  return static_cast<crc32c_t>(crc ^ kCRC32Xor);

}

// Called by `absl::ExtendCrc32c()` on strings with size > 64 or when hardware

// CRC32C support is missing.

crc32c_t ExtendCrc32cInternal(crc32c_t initial_crc,

                              absl::string_view buf_to_add) {

  uint32_t crc = static_cast<uint32_t>(initial_crc) ^ kCRC32Xor;

  CrcEngine()->Extend(&crc, buf_to_add.data(), buf_to_add.size());

  return static_cast<crc32c_t>(crc ^ kCRC32Xor);

}

}  // namespace crc_internal

crc32c_t ExtendCrc32cByZeroes(crc32c_t initial_crc, size_t length) {

  uint32_t crc = static_cast<uint32_t>(initial_crc) ^ kCRC32Xor;

  CrcEngine()->ExtendByZeroes(&crc, length);

  return static_cast<crc32c_t>(crc ^ kCRC32Xor);

}

crc32c_t ConcatCrc32c(crc32c_t lhs_crc, crc32c_t rhs_crc, size_t rhs_len) {

  uint32_t result = static_cast<uint32_t>(lhs_crc);

  CrcEngine()->ExtendByZeroes(&result, rhs_len);

  return crc32c_t{result ^ static_cast<uint32_t>(rhs_crc)};

}

crc32c_t RemoveCrc32cPrefix(crc32c_t crc_a, crc32c_t crc_ab, size_t length_b) {

  return ConcatCrc32c(crc_a, crc_ab, length_b);

}

crc32c_t MemcpyCrc32c(void* dest, const void* src, size_t count,

                      crc32c_t initial_crc) {

  return static_cast<crc32c_t>(

      crc_internal::Crc32CAndCopy(dest, src, count, initial_crc, false));

}

// Remove a Suffix of given size from a buffer

//

// Given a CRC32C of an existing buffer, `full_string_crc`; the CRC32C of a

// suffix of that buffer to remove, `suffix_crc`; and suffix buffer's length,

// `suffix_len` return the CRC32C 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_len) {

  uint32_t result = static_cast<uint32_t>(full_string_crc) ^

                    static_cast<uint32_t>(suffix_crc);

  CrcEngine()->UnextendByZeroes(&result, suffix_len);

  return crc32c_t{result};

}

ABSL_NAMESPACE_END

}  // namespace absl