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#include "cru/common/StringUtil.hpp"
namespace cru {
template <typename UInt, int number_of_bit>
inline std::enable_if_t<std::is_unsigned_v<UInt>, CodePoint> ExtractBits(
UInt n) {
return static_cast<CodePoint>(n & ((1u << number_of_bit) - 1));
}
CodePoint Utf8Iterator::Next() {
if (position_ == static_cast<Index>(string_.length()))
return k_code_point_end;
const auto cu0 = static_cast<std::uint8_t>(string_[position_++]);
auto read_next_folowing_code = [this]() -> CodePoint {
if (this->position_ == static_cast<Index>(string_.length()))
throw TextEncodeException(
"Unexpected end when read continuing byte of multi-byte code point.");
#ifdef CRU_DEBUG
const auto u = static_cast<std::uint8_t>(string_[position_]);
if (!(u & (1u << 7)) || (u & (1u << 6))) {
throw TextEncodeException(
"Unexpected bad-format (not 0b10xxxxxx) continuing byte of "
"multi-byte code point.");
}
#endif
return ExtractBits<std::uint8_t, 6>(string_[position_++]);
};
if ((1u << 7) & cu0) {
if ((1u << 6) & cu0) { // 2~4-length code point
if ((1u << 5) & cu0) { // 3~4-length code point
if ((1u << 4) & cu0) { // 4-length code point
#ifdef CRU_DEBUG
if (cu0 & (1u << 3)) {
throw TextEncodeException(
"Unexpected bad-format begin byte (not 0b10xxxxxx) of 4-byte "
"code point.");
}
#endif
const CodePoint s0 = ExtractBits<std::uint8_t, 3>(cu0) << (6 * 3);
const CodePoint s1 = read_next_folowing_code() << (6 * 2);
const CodePoint s2 = read_next_folowing_code() << 6;
const CodePoint s3 = read_next_folowing_code();
return s0 + s1 + s2 + s3;
} else { // 3-length code point
const CodePoint s0 = ExtractBits<std::uint8_t, 4>(cu0) << (6 * 2);
const CodePoint s1 = read_next_folowing_code() << 6;
const CodePoint s2 = read_next_folowing_code();
return s0 + s1 + s2;
}
} else { // 2-length code point
const CodePoint s0 = ExtractBits<std::uint8_t, 5>(cu0) << 6;
const CodePoint s1 = read_next_folowing_code();
return s0 + s1;
}
} else {
throw TextEncodeException(
"Unexpected bad-format (0b10xxxxxx) begin byte of a code point.");
}
} else {
return static_cast<CodePoint>(cu0);
}
}
} // namespace cru
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