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Introduce utility class for encoding
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| /* | ||
| * Copyright (c) Facebook, Inc. and its 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 | ||
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| #include <exception> | ||
| #include <map> | ||
| #include <string> | ||
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| #include <folly/Range.h> | ||
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| #include "velox/common/base/Exceptions.h" | ||
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| namespace facebook::velox::encoding { | ||
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| const size_t kCharsetSize = 64; | ||
| const size_t kReverseIndexSize = 256; | ||
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| /// Character set used for encoding purposes. | ||
| /// Contains specific characters that form the encoding scheme. | ||
| using Charset = std::array<char, kCharsetSize>; | ||
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| /// Reverse lookup table for decoding purposes. | ||
| /// Maps each possible encoded character to its corresponding numeric value | ||
| /// within the encoding base. | ||
| using ReverseIndex = std::array<uint8_t, kReverseIndexSize>; | ||
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| /// Padding character used in encoding. | ||
| const static char kPadding = '='; | ||
| /// Checks if there is padding in encoded data. | ||
| static inline bool isPadded(const char* data, size_t len) { | ||
| return (len > 0 && data[len - 1] == kPadding) ? true : false; | ||
| } | ||
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| /// Counts the number of padding characters in encoded data. | ||
| static inline size_t numPadding(const char* src, size_t len) { | ||
| size_t numPadding{0}; | ||
| while (len > 0 && src[len - 1] == kPadding) { | ||
| numPadding++; | ||
| len--; | ||
| } | ||
| return numPadding; | ||
| } | ||
| /// Performs a reverse lookup in the reverse index to retrieve the original | ||
| /// index of a character in the base. | ||
| inline uint8_t | ||
| baseReverseLookup(int base, char p, const ReverseIndex& reverseIndex) { | ||
| auto curr = reverseIndex[(uint8_t)p]; | ||
| if (curr >= base) { | ||
| VELOX_USER_FAIL("decode() - invalid input string: invalid characters"); | ||
| } | ||
| return curr; | ||
| } | ||
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| // Validate the character in charset with ReverseIndex table | ||
| static constexpr bool checkForwardIndex( | ||
| uint8_t idx, | ||
| const Charset& charset, | ||
| const ReverseIndex& reverseIndex) { | ||
| for (uint8_t i = 0; i <= idx; ++i) { | ||
| if (!(reverseIndex[static_cast<uint8_t>(charset[i])] == i)) { | ||
| return false; | ||
| } | ||
| } | ||
| return true; | ||
| } | ||
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| /// Searches for a character within a charset up to a certain index. | ||
| static const bool findCharacterInCharSet( | ||
| const Charset& charset, | ||
| int base, | ||
| uint8_t idx, | ||
| const char c) { | ||
| for (; idx < base; ++idx) { | ||
| if (charset[idx] == c) { | ||
| return true; | ||
| } | ||
| } | ||
| return false; | ||
| } | ||
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| /// Checks the consistency of a reverse index mapping for a given character | ||
| /// set. | ||
| static constexpr bool checkReverseIndex( | ||
| uint8_t idx, | ||
| int base, | ||
| const Charset& charset, | ||
| const ReverseIndex& reverseIndex) { | ||
| for (uint8_t currentIdx = idx; currentIdx != static_cast<uint8_t>(-1); | ||
| --currentIdx) { | ||
| if (reverseIndex[currentIdx] == 255) { | ||
| if (findCharacterInCharSet( | ||
| charset, base, 0, static_cast<char>(currentIdx))) { | ||
| return false; | ||
| } | ||
| } else { | ||
| if (!(charset[reverseIndex[currentIdx]] == currentIdx)) { | ||
| return false; | ||
| } | ||
| } | ||
| } | ||
| return true; | ||
| } | ||
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| } // namespace facebook::velox::encoding |
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