BaseEncoding.h

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/*
 * This file is part of the TrinityCore Project. See AUTHORS file for Copyright information
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2 of the License, or (at your
 * option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program. If not, see <http://www.gnu.org/licenses/>.
 */
 
#ifndef TRINITY_BASE_ENCODING_HPP
#define TRINITY_BASE_ENCODING_HPP
 
#include "Define.h"
#include "Optional.h"
#include <numeric>
#include <string>
#include <string_view>
#include <vector>
 
namespace Trinity
{
namespace Impl
{
template <typename Encoding>
struct GenericBaseEncoding
{
 static constexpr std::size_t BITS_PER_CHAR = Encoding::BITS_PER_CHAR;
 static constexpr std::size_t PAD_TO = std::lcm(8u, BITS_PER_CHAR);
 
 static_assert(BITS_PER_CHAR < 8, "Encoding parameters are invalid");
 
 static constexpr uint8 DECODE_ERROR = Encoding::DECODE_ERROR;
 static constexpr char PADDING = Encoding::PADDING;
 
 static constexpr std::size_t EncodedSize(std::size_t size)
 {
 size *= 8; // bits in input
 if (size % PAD_TO) // pad to boundary
 size += (PAD_TO - (size % PAD_TO));
 return (size / BITS_PER_CHAR);
 }
 
 static constexpr std::size_t DecodedSize(std::size_t size)
 {
 size *= BITS_PER_CHAR; // bits in input
 if (size % PAD_TO) // pad to boundary
 size += (PAD_TO - (size % PAD_TO));
 return (size / 8);
 }
 
 static std::string Encode(std::vector<uint8> const& data)
 {
 auto it = data.begin(), end = data.end();
 if (it == end)
 return "";
 
 std::string s;
 s.reserve(EncodedSize(data.size()));
 
 uint8 bitsLeft = 8; // in current byte
 do
 {
 uint8 thisC = 0;
 if (bitsLeft >= BITS_PER_CHAR)
 {
 bitsLeft -= BITS_PER_CHAR;
 thisC = ((*it >> bitsLeft) & ((1 << BITS_PER_CHAR)-1));
 if (!bitsLeft)
 {
 ++it;
 bitsLeft = 8;
 }
 }
 else
 {
 thisC = (*it & ((1 << bitsLeft) - 1)) << (BITS_PER_CHAR - bitsLeft);
 bitsLeft += (8 - BITS_PER_CHAR);
 if ((++it) != end)
 thisC |= (*it >> bitsLeft);
 }
 s.append(1, Encoding::Encode(thisC));
 } while (it != end);
 
 while (bitsLeft != 8)
 {
 if (bitsLeft > BITS_PER_CHAR)
 bitsLeft -= BITS_PER_CHAR;
 else
 bitsLeft += (8 - BITS_PER_CHAR);
 s.append(1, PADDING);
 }
 
 return s;
 }
 
 static Optional<std::vector<uint8>> Decode(std::string_view data)
 {
 auto it = data.begin(), end = data.end();
 if (it == end)
 return std::vector<uint8>();
 
 std::vector<uint8> v;
 v.reserve(DecodedSize(data.size()));
 
 uint8 currentByte = 0;
 uint8 bitsLeft = 8; // in current byte
 while ((it != end) && (*it != PADDING))
 {
 uint8 cur = Encoding::Decode(*(it++));
 if (cur == DECODE_ERROR)
 return {};
 
 if (bitsLeft > BITS_PER_CHAR)
 {
 bitsLeft -= BITS_PER_CHAR;
 currentByte |= (cur << bitsLeft);
 }
 else
 {
 bitsLeft = BITS_PER_CHAR - bitsLeft; // in encoded char
 currentByte |= (cur >> bitsLeft);
 v.push_back(currentByte);
 currentByte = (cur & ((1 << bitsLeft) - 1));
 bitsLeft = 8 - bitsLeft; // in byte again
 currentByte <<= bitsLeft;
 }
 }
 
 if (currentByte)
 return {}; // decode error, trailing non-zero bits
 
 // process padding
 while ((it != end) && (*it == PADDING) && (bitsLeft != 8))
 {
 if (bitsLeft > BITS_PER_CHAR)
 bitsLeft -= BITS_PER_CHAR;
 else
 bitsLeft += (8 - BITS_PER_CHAR);
 ++it;
 }
 
 // ok, all padding should be consumed, and we should be at end of string
 if (it == end)
 return v;
 
 // anything else is an error
 return {};
 }
};
}
}
 
#endif