| // Copyright 2019 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #include "components/base32/base32_test_util.h" |
| |
| #include <stddef.h> |
| |
| #include <limits> |
| |
| #include "base/logging.h" |
| #include "base/numerics/safe_math.h" |
| #include "components/base32/base32.h" |
| |
| namespace base32 { |
| |
| namespace { |
| |
| // Returns a 5 bit number between [0,31] matching the provided base 32 encoded |
| // character. Returns 0xff on error. |
| uint8_t ReverseMapping(char input_char) { |
| if (input_char >= 'A' && input_char <= 'Z') |
| return input_char - 'A'; |
| if (input_char >= '2' && input_char <= '7') |
| return input_char - '2' + 26; |
| |
| NOTREACHED() << "Invalid base32 character"; |
| return 0xff; |
| } |
| |
| } // namespace |
| |
| std::string Base32Decode(base::StringPiece input) { |
| if (input.empty()) |
| return std::string(); |
| |
| // Remove padding, if any |
| const size_t padding_index = input.find(kPaddingChar); |
| if (padding_index != base::StringPiece::npos) |
| input.remove_suffix(input.size() - padding_index); |
| |
| const size_t decoded_length = |
| (base::MakeCheckedNum(input.size()) * 5 / 8).ValueOrDie(); |
| |
| std::string output; |
| output.reserve(decoded_length); |
| |
| // A bit stream which will be read from the left and appended to from the |
| // right as it's emptied. |
| uint16_t bit_stream = 0; |
| size_t free_bits = 16; |
| for (char input_char : input) { |
| const uint8_t decoded_5bits = ReverseMapping(input_char); |
| // If an invalid character is read from the input, then stop decoding. |
| if (decoded_5bits >= 32) |
| return std::string(); |
| |
| // Place the next decoded 5-bits in the stream. |
| bit_stream |= decoded_5bits << (free_bits - 5); |
| free_bits -= 5; |
| |
| // If the stream is filled with a byte, flush the stream of that byte and |
| // append it to the output. |
| if (free_bits <= 8) { |
| output.push_back(static_cast<char>(bit_stream >> 8)); |
| bit_stream <<= 8; |
| free_bits += 8; |
| } |
| } |
| |
| DCHECK_EQ(decoded_length, output.size()); |
| return output; |
| } |
| |
| } // namespace base32 |