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#ifndef SIMDUTF_VALID_UTF16_TO_UTF8_H
#define SIMDUTF_VALID_UTF16_TO_UTF8_H
namespace simdutf {
namespace scalar {
namespace {
namespace utf16_to_utf8 {
template <endianness big_endian>
inline size_t convert_valid(const char16_t *buf, size_t len,
char *utf8_output) {
const uint16_t *data = reinterpret_cast<const uint16_t *>(buf);
size_t pos = 0;
char *start{utf8_output};
while (pos < len) {
// try to convert the next block of 4 ASCII characters
if (pos + 4 <=
len) { // if it is safe to read 8 more bytes, check that they are ascii
uint64_t v;
::memcpy(&v, data + pos, sizeof(uint64_t));
if (!match_system(big_endian)) {
v = (v >> 8) | (v << (64 - 8));
}
if ((v & 0xFF80FF80FF80FF80) == 0) {
size_t final_pos = pos + 4;
while (pos < final_pos) {
*utf8_output++ = !match_system(big_endian)
? char(utf16::swap_bytes(buf[pos]))
: char(buf[pos]);
pos++;
}
continue;
}
}
uint16_t word =
!match_system(big_endian) ? utf16::swap_bytes(data[pos]) : data[pos];
if ((word & 0xFF80) == 0) {
// will generate one UTF-8 bytes
*utf8_output++ = char(word);
pos++;
} else if ((word & 0xF800) == 0) {
// will generate two UTF-8 bytes
// we have 0b110XXXXX 0b10XXXXXX
*utf8_output++ = char((word >> 6) | 0b11000000);
*utf8_output++ = char((word & 0b111111) | 0b10000000);
pos++;
} else if ((word & 0xF800) != 0xD800) {
// will generate three UTF-8 bytes
// we have 0b1110XXXX 0b10XXXXXX 0b10XXXXXX
*utf8_output++ = char((word >> 12) | 0b11100000);
*utf8_output++ = char(((word >> 6) & 0b111111) | 0b10000000);
*utf8_output++ = char((word & 0b111111) | 0b10000000);
pos++;
} else {
// must be a surrogate pair
uint16_t diff = uint16_t(word - 0xD800);
if (pos + 1 >= len) {
return 0;
} // minimal bound checking
uint16_t next_word = !match_system(big_endian)
? utf16::swap_bytes(data[pos + 1])
: data[pos + 1];
uint16_t diff2 = uint16_t(next_word - 0xDC00);
uint32_t value = (diff << 10) + diff2 + 0x10000;
// will generate four UTF-8 bytes
// we have 0b11110XXX 0b10XXXXXX 0b10XXXXXX 0b10XXXXXX
*utf8_output++ = char((value >> 18) | 0b11110000);
*utf8_output++ = char(((value >> 12) & 0b111111) | 0b10000000);
*utf8_output++ = char(((value >> 6) & 0b111111) | 0b10000000);
*utf8_output++ = char((value & 0b111111) | 0b10000000);
pos += 2;
}
}
return utf8_output - start;
}
} // namespace utf16_to_utf8
} // unnamed namespace
} // namespace scalar
} // namespace simdutf
#endif
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