absl/crc/internal/crc32c_inline.h

// 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.

#ifndef ABSL_CRC_INTERNAL_CRC32C_INLINE_H_
#define ABSL_CRC_INTERNAL_CRC32C_INLINE_H_

#include <cstdint>

#include "absl/base/config.h"
#include "absl/base/internal/endian.h"
#include "absl/crc/internal/crc32_x86_arm_combined_simd.h"

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace crc_internal {

// CRC32C implementation optimized for small inputs.
// Either computes crc and return true, or if there is
// no hardware support does nothing and returns false.
inline bool ExtendCrc32cInline(uint32_t* crc, const char* p, size_t n) {
#if defined(ABSL_CRC_INTERNAL_HAVE_ARM_SIMD) || \
    defined(ABSL_CRC_INTERNAL_HAVE_X86_SIMD)
  constexpr uint32_t kCrc32Xor = 0xffffffffU;
  *crc ^= kCrc32Xor;
  if (n & 1) {
    *crc = CRC32_u8(*crc, static_cast<uint8_t>(*p));
    n--;
    p++;
  }
  if (n & 2) {
    *crc = CRC32_u16(*crc, absl::little_endian::Load16(p));
    n -= 2;
    p += 2;
  }
  if (n & 4) {
    *crc = CRC32_u32(*crc, absl::little_endian::Load32(p));
    n -= 4;
    p += 4;
  }
  while (n) {
    *crc = CRC32_u64(*crc, absl::little_endian::Load64(p));
    n -= 8;
    p += 8;
  }
  *crc ^= kCrc32Xor;
  return true;
#else
  // No hardware support, signal the need to fallback.
  static_cast<void>(crc);
  static_cast<void>(p);
  static_cast<void>(n);
  return false;
#endif  // defined(ABSL_CRC_INTERNAL_HAVE_ARM_SIMD) ||
        // defined(ABSL_CRC_INTERNAL_HAVE_X86_SIMD)
}

}  // namespace crc_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_CRC_INTERNAL_CRC32C_INLINE_H_