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libcruft-util/cruft/util/encode/base.hpp

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/*
relicense under MPL-2.0
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* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
* Copyright 2017 Danny Robson <danny@nerdcruft.net>
*/
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#pragma once
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#include "../view.hpp"
#include <cstdint>
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namespace cruft::encode {
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///////////////////////////////////////////////////////////////////////////
template <int Size>
struct alphabet {
static const char enc[Size];
static const uint8_t dec[256];
};
///////////////////////////////////////////////////////////////////////////
template <>
const char alphabet<64>::enc[64] = {
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/',
};
//-------------------------------------------------------------------------
template <>
const uint8_t alphabet<64>::dec[256] = {
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x3E, 0, 0, 0, 0x3F,
0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3A, 0x3B, 0x3C, 0x3D, 0, 0, 0, 0, 0, 0,
0, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E,
0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0, 0, 0, 0, 0,
0, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28,
0x29, 0x2A, 0x2B, 0x2C, 0x2D, 0x2E, 0x2F, 0x30, 0x31, 0x32, 0x33, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
};
///////////////////////////////////////////////////////////////////////////
template <>
const char alphabet<32>::enc[32] {
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
'2', '3', '4', '5', '6', '7',
};
//-------------------------------------------------------------------------
template <>
const uint8_t alphabet<32>::dec[256] = {
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e,
0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
};
///////////////////////////////////////////////////////////////////////////
template <>
const char alphabet<16>::enc[16] {
'0', '1', '2', '3', '4', '5', '6', '7',
'8', '9', 'A', 'B', 'C', 'D', 'E', 'F',
};
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//-------------------------------------------------------------------------
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template <>
const uint8_t alphabet<16>::dec[256] = {
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0, 0, 0, 0, 0, 0,
0, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
};
//-------------------------------------------------------------------------
template <int Size> constexpr auto enc_v = alphabet<Size>::enc;
template <int Size> constexpr auto dec_v = alphabet<Size>::dec;
///////////////////////////////////////////////////////////////////////////
/// rfc4648 base16, base32, and base64 encoding
template <int Size>
struct base {
static constexpr auto symbol_bits = log2 (Size);
static constexpr auto group_bits = std::lcm (symbol_bits, 8);
static constexpr auto group_symbols = group_bits / symbol_bits;
static constexpr auto group_bytes = group_bits / 8;
static constexpr uint_fast32_t mask = (1<<symbol_bits)-1;
template <typename InputT, typename OutputT>
static OutputT
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encode (OutputT dst, const cruft::view<InputT> src)
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{
// convert whole groups of symbols while we have enough bytes remaining
auto cursor = std::cbegin (src);
for (size_t i = 0, last = std::size (src) / group_bytes; i != last; ++i) {
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auto const tally = std::accumulate (
cursor,
cursor + group_bytes,
uint64_t {0},
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[] (auto a, auto b) { return a << 8 | b; }
);
cursor += group_bytes;
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for (int j = group_symbols - 1; j >= 0; --j) {
auto const shift = j * symbol_bits;
auto const upper = tally >> shift;
*dst++ = enc_v<Size>[upper & mask];
}
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}
// we don't need to pad the output so we can early exit
if (cursor == std::cend (src))
return dst;
// accumulate the remaining bits and pad to a multiple of the
// output group length
auto tally = std::accumulate (
cursor,
std::cend (src),
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uint64_t {0},
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[] (auto a, auto b) { return a << 8 | b; }
);
auto input_remain = std::cend (src) - cursor;
tally <<= symbol_bits - input_remain * 8 % symbol_bits;
// write each of the remaining symbols
auto output_remain = (input_remain * 8 + symbol_bits - 1) / symbol_bits;
for (auto i = output_remain - 1; i >= 0; --i)
*dst++ = enc_v<Size>[tally >> (i * symbol_bits) & mask];
// pad the output to the symbol group size with '=' characters
auto fill = (group_bytes - input_remain) * 8 / symbol_bits;
return std::fill_n (dst, fill, '=');
}
//---------------------------------------------------------------------
template <typename InputT, typename OutputT>
static OutputT
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decode (OutputT dst, cruft::view<InputT> src)
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{
if (src.empty ())
return dst;
if (src.size () % group_symbols)
throw std::invalid_argument ("base-encoded strings must be a proper multiple of symbols");
auto cursor = std::cbegin (src);
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const auto groups = std::size (src) / group_symbols;
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const bool padded = std::cend (src)[-1] == '=';
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for (size_t i = 0; i < groups - (padded?1:0); ++i) {
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uint64_t accum = 0;
for (int j = 0; j < group_symbols; ++j) {
auto symbol = dec_v<Size>[unsigned(*cursor++)];
accum <<= symbol_bits;
accum |= symbol;
}
for (int j = group_bytes - 1; j >= 0; --j) {
const uint8_t byte = accum >> (j*8);
*dst++ = byte;
}
}
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if (padded) {
uint64_t accum = 0;
int symbols = 0;
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for (int j = 0; j < group_symbols; ++j) {
auto symbol = *cursor++;
if (symbol == '=')
break;
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symbols++;
accum <<= symbol_bits;
accum |= dec_v<Size>[unsigned(symbol)];
}
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auto bits = symbols * symbol_bits;
auto shift = bits%8;
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accum >>= shift;
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for (int j = bits / 8 - 1; j >= 0; --j) {
auto byte = (accum >> (j*8)) & 0xff;
*dst++ = byte;
}
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}
return dst;
}
};
};
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