folly/folly/detail/base64_detail/Base64HiddenConstants.h

/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * 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
 *
 *     http://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.
 */

#pragma once

#include <array>
#include <cstdint>
#include <limits>
#include <folly/detail/base64_detail/Base64Constants.h>

namespace folly::detail::base64_detail::constants {

// Some constants we have to expose for everyone in order to
// support constexpr operations.
// These we can internalize.

// SWAR -----------------------------------------

constexpr std::uint32_t kSwarDecodeErrorMarker = …;

template <typename DecodeChar>
constexpr std::array<std::array<std::uint32_t, 256>, 4> buildSWARDecodeTable(
    DecodeChar decodeChar) { … }

constexpr auto kBase64SwarDecodeTable = …;
constexpr auto kBase64SwarURLDecodeTable = …;

// Simd -----------------------------------------

// clang-format off
constexpr std::array<std::int8_t, 16> kEncodeTable { … };
// clang-format on

constexpr auto kEncodeURLTable = …auto res = …;

constexpr auto kValidHighByLowNibble = …auto build = …::uint8_t nibblesArr[] = …::uint8_t res = …::uint8_t nibble : nibblesArr) { … }
    return res;
  };

  std::array<std::uint8_t, 16> res{ … };

  res[0] = …int i = …;

// clang-format off
constexpr std::array<std::int8_t, 16> kOffsetByHighNibbleDecodeTable { … };
// clang-format on

} // namespace folly::detail::base64_detail::constants