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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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| namespace facebook::velox::encoding { | ||
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| class EncoderException : public std::exception { | ||
| public: | ||
| explicit EncoderException(const char* msg) : msg_(msg) {} | ||
| const char* what() const noexcept override { | ||
| return msg_; | ||
| } | ||
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| protected: | ||
| const char* msg_; | ||
| }; | ||
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| using Charset = std::array<char, 64>; | ||
| using ReverseIndex = std::array<uint8_t, 256>; | ||
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| // Padding character used in encoding | ||
| constexpr static char kPadding = '='; | ||
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| // Checks is there padding in encoded data | ||
| 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. | ||
| inline size_t countPadding(const char* src, size_t len) { | ||
| size_t padding_count = 0; | ||
| while (len > 0 && src[len - 1] == kPadding) { | ||
| padding_count++; | ||
| len--; | ||
| } | ||
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| return padding_count; | ||
| } | ||
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| // Gets value corresponding to an encoded character | ||
| inline uint8_t | ||
| baseReverseLookup(int base, char p, const ReverseIndex& reverse_lookup) { | ||
| auto curr = reverse_lookup[(uint8_t)p]; | ||
| // Value of encoded character shall be less than base. | ||
| if (curr >= base) { | ||
| throw EncoderException( | ||
| "decode() - invalid input string: invalid characters"); | ||
| } | ||
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| return curr; | ||
| } | ||
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| // Validate the character in charset with ReverseIndex table | ||
| constexpr bool checkForwardIndex( | ||
| uint8_t idx, | ||
| const Charset& charset, | ||
| const ReverseIndex& table) { | ||
| return (table[static_cast<uint8_t>(charset[idx])] == idx) && | ||
| (idx > 0 ? checkForwardIndex(idx - 1, charset, table) : true); | ||
| } | ||
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| /// Similar to strchr(), but for null-terminated const strings. | ||
| /// Another difference is that we do not consider "\0" to be present in the | ||
| /// string. | ||
| /// Returns true if "str" contains the character c. | ||
| constexpr bool findCharacterInCharSet( | ||
| const Charset& charset, | ||
| int base, | ||
| uint8_t idx, | ||
| const char c) { | ||
| return idx < base && | ||
| ((charset[idx] == c) || | ||
| findCharacterInCharSet(charset, base, idx + 1, c)); | ||
| } | ||
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| // Validate the value in ReverseIndex table with charset. | ||
| constexpr bool checkReverseIndex( | ||
| uint8_t idx, | ||
| const Charset& charset, | ||
| int base, | ||
| const ReverseIndex& table) { | ||
| return (table[idx] == 255 ? !findCharacterInCharSet( | ||
| charset, base, 0, static_cast<char>(idx)) | ||
| : (charset[table[idx]] == idx)) && | ||
| (idx > 0 ? checkReverseIndex(idx - 1, charset, base, table) : true); | ||
| } | ||
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| } // namespace facebook::velox::encoding |
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