| // Copyright 2016 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.h" |
| |
| #include <stddef.h> |
| #include <algorithm> |
| #include <limits> |
| |
| #include "base/logging.h" |
| |
| namespace base32 { |
| |
| namespace { |
| constexpr char kEncoding[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"; |
| } // namespace |
| |
| std::string Base32Encode(base::StringPiece input, Base32EncodePolicy policy) { |
| if (input.empty()) |
| return std::string(); |
| |
| if (input.size() > std::numeric_limits<size_t>::max() / 8) { |
| NOTREACHED() |
| << "Input is too large and would overflow encoded size computation."; |
| return std::string(); |
| } |
| |
| // Per RFC4648, the output is formed of 8 characters per 40 bits of input and |
| // another 8 characters for the last group of [1,39] bits in the input. |
| // That is: ceil(input.size() * 8.0 / 40.0) * 8 == |
| // ceil(input.size() / 5.0) * 8 == |
| // ((input.size() + 4) / 5) * 8. |
| const size_t padded_length = ((input.size() + 4) / 5) * 8; |
| |
| // When no padding is used, the output is exactly 1 character per 5 bits of |
| // input and one more for the last [1,4] bits. |
| // That is: ceil(input.size() * 8.0 / 5.0) == |
| // (input.size() * 8 + 4) / 5. |
| const size_t unpadded_length = (input.size() * 8 + 4) / 5; |
| |
| std::string output; |
| const size_t encoded_length = policy == Base32EncodePolicy::INCLUDE_PADDING |
| ? padded_length |
| : unpadded_length; |
| output.reserve(encoded_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 = (static_cast<uint8_t>(input[0]) << 8); |
| size_t next_byte_index = 1; |
| int free_bits = 8; |
| while (free_bits < 16) { |
| // Extract the 5 leftmost bits in the stream |
| output.push_back(kEncoding[(bit_stream & 0xf800) >> 11]); |
| bit_stream <<= 5; |
| free_bits += 5; |
| |
| // If there is enough room in the bit stream, inject another byte (if there |
| // are any left...). |
| if (free_bits >= 8 && next_byte_index < input.size()) { |
| free_bits -= 8; |
| bit_stream += static_cast<uint8_t>(input[next_byte_index++]) << free_bits; |
| } |
| } |
| |
| if (policy == Base32EncodePolicy::INCLUDE_PADDING) { |
| output.append(padded_length - unpadded_length, '='); |
| } |
| |
| DCHECK_EQ(encoded_length, output.size()); |
| return output; |
| } |
| |
| } // namespace base32 |