Function from_utf16

example/cacheHierarchy/fkYAML/node.hpp:2001–2042

@brief Converts UTF-16 encoded characters to UTF-8 encoded bytes. @param[in] utf16 UTF-16 encoded character(s). @param[out] utf8 UTF-8 encoded bytes. @param[out] consumed_size The number of UTF-16 encoded characters used for the conversion. @param[out] encoded_size The size of UTF-encoded bytes.

/// @param[out] consumed_size The number of UTF-16 encoded characters used for the conversion.
/// @param[out] encoded_size The size of UTF-encoded bytes.
inline void from_utf16(
    std::array<char16_t, 2> utf16, std::array<uint8_t, 4>& utf8, uint32_t& consumed_size, uint32_t& encoded_size) {
    const auto first = utf16[0];
    const auto second = utf16[1];
    if (first < 0x80u) {
        utf8[0] = static_cast<uint8_t>(first & 0x7Fu);
        consumed_size = 1;
        encoded_size = 1;
    }
    else if (first <= 0x7FFu) {
        const auto utf8_chunk = static_cast<uint16_t>(0xC080u | ((first & 0x07C0u) << 2) | (first & 0x3Fu));
        utf8[0] = static_cast<uint8_t>(utf8_chunk >> 8);
        utf8[1] = static_cast<uint8_t>(utf8_chunk);
        consumed_size = 1;
        encoded_size = 2;
    }
    else if (first < 0xD800u || 0xE000u <= first) {
        const auto utf8_chunk =
            static_cast<uint32_t>(0xE08080u | ((first & 0xF000u) << 4) | ((first & 0x0FC0u) << 2) | (first & 0x3Fu));
        utf8[0] = static_cast<uint8_t>(utf8_chunk >> 16);
        utf8[1] = static_cast<uint8_t>(utf8_chunk >> 8);
        utf8[2] = static_cast<uint8_t>(utf8_chunk);
        consumed_size = 1;
        encoded_size = 3;
    }
    else if (first <= 0xDBFFu && 0xDC00u <= second && second <= 0xDFFFu) {
        // surrogate pair
        const uint32_t code_point = 0x10000u + ((first & 0x03FFu) << 10) + (second & 0x03FFu);
        const auto utf8_chunk = static_cast<uint32_t>(
            0xF0808080u | ((code_point & 0x1C0000u) << 6) | ((code_point & 0x03F000u) << 4) |
            ((code_point & 0x0FC0u) << 2) | (code_point & 0x3Fu));
        utf8[0] = static_cast<uint8_t>(utf8_chunk >> 24);
        utf8[1] = static_cast<uint8_t>(utf8_chunk >> 16);
        utf8[2] = static_cast<uint8_t>(utf8_chunk >> 8);
        utf8[3] = static_cast<uint8_t>(utf8_chunk);
        consumed_size = 2;
        encoded_size = 4;
    }
    else {
        throw invalid_encoding("Invalid UTF-16 encoding detected.", utf16);
    }
}

/// @brief Converts a UTF-32 encoded character to UTF-8 encoded bytes.
/// @param[in] utf32 A UTF-32 encoded character.