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#include <algorithm>
#include <cstdint>
#include <ranges>
#include <string_view>
// @brief Adaptor that converts its std::byte input range into a hexadecimal character view.
//
// Usage example:
//
// \code{.cpp}
// std::array{std::byte{1}, std::byte{2}, std::byte{10}} | encode16 // will generate view on "01020A"sv
// \endcode
inline constexpr auto encode16 = [] {
using namespace std::literals;
using namespace std::views;
return transform([](std::byte byte) {
return iota(0, 2) | reverse | transform([byte](int i) -> uint8_t {
return (static_cast<uint8_t>(byte) >> (4 * i)) & 0xF;
});
}) |
join | transform([](uint8_t nible) -> char { return "0123456789ABCDEF"sv.at(nible); });
}();
// @brief Adaptor that converts its char input range into a std::byte range view.
//
// @warning Does not validate its input! Any invalid character will be transformed into a zero nibble. Do not use on
// non validated input if validation matters!
//
// Usage example:
//
// \code{.cpp}
// "01020A"sv | decode16 // will generate view on std::array{std::byte{1}, std::byte{2}, std::byte{10}}
// \endcode
inline constexpr auto decode16 = [] {
using namespace std::views;
return transform([](char hex) -> uint8_t {
static constexpr auto u = std::bit_cast<char, uint8_t>;
static constexpr auto lookup = [] -> std::array<uint8_t, 0xFF> {
std::array<uint8_t, 0xFF> a{};
a[u('0')] = 0x0, a[u('1')] = 0x1, a[u('2')] = 0x2, a[u('3')] = 0x3, a[u('4')] = 0x4,
a[u('5')] = 0x5, a[u('6')] = 0x6, a[u('7')] = 0x7, a[u('8')] = 0x8, a[u('9')] = 0x9,
a[u('A')] = 0xA, a[u('B')] = 0xB, a[u('C')] = 0xC, a[u('D')] = 0xD, a[u('E')] = 0xE,
a[u('F')] = 0xF, a[u('a')] = 0xA, a[u('b')] = 0xB, a[u('c')] = 0xC, a[u('d')] = 0xD,
a[u('e')] = 0xE, a[u('f')] = 0xF;
return a;
}();
return lookup.at(u(hex));
}) |
chunk(2) | transform([](auto &&pair) -> std::byte {
return static_cast<std::byte>(std::ranges::fold_left(
pair, 0, [](uint8_t n1, uint8_t n2) -> uint8_t { return (n1 << 4) | n2; }));
});
}();
auto main() -> int
{
using namespace std::literals;
using namespace std::views;
using std::ranges::equal;
constexpr auto to_bytes = transform([](uint8_t num) -> std::byte { return static_cast<std::byte>(num); });
static_assert(equal(std::array{1, 192, 255, 238} | to_bytes | encode16, "01C0FFEE"sv));
static_assert(equal("01C0ffee"sv | decode16, std::array{1, 192, 255, 238} | to_bytes));
static_assert(equal(std::array{0x01, 0x23, 0x45, 0x67, 0x89, 0xAB, 0xCD, 0xEF} | to_bytes | encode16,
"0123456789ABCDEF"sv));
static_assert(equal("0123456789aBCdEf"sv | decode16,
std::array{0x01, 0x23, 0x45, 0x67, 0x89, 0xAB, 0xCD, 0xEF} | to_bytes));
static_assert(equal(std::array{1, 192, 255, 238} | to_bytes | encode16 | decode16,
std::array{1, 192, 255, 238} | to_bytes));
static_assert(equal("01C0ffee"sv | decode16 | encode16, "01C0FFEE"sv));
static_assert(equal(std::array{0x01, 0x23, 0x45, 0x67, 0x89, 0xAB, 0xCD, 0xEF} | to_bytes | encode16 | decode16,
std::array{0x01, 0x23, 0x45, 0x67, 0x89, 0xAB, 0xCD, 0xEF} | to_bytes));
static_assert(equal("0123456789aBCdEf"sv | decode16 | encode16, "0123456789ABCDEF"sv));
return 0;
}
