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#ifndef SIMDUTF_UTF8_TO_LATIN1_H
#define SIMDUTF_UTF8_TO_LATIN1_H
namespace simdutf {
namespace scalar {
namespace {
namespace utf8_to_latin1 {
inline size_t convert(const char *buf, size_t len, char *latin_output) {
const uint8_t *data = reinterpret_cast<const uint8_t *>(buf);
size_t pos = 0;
char *start{latin_output};
while (pos < len) {
// try to convert the next block of 16 ASCII bytes
if (pos + 16 <=
len) { // if it is safe to read 16 more bytes, check that they are ascii
uint64_t v1;
::memcpy(&v1, data + pos, sizeof(uint64_t));
uint64_t v2;
::memcpy(&v2, data + pos + sizeof(uint64_t), sizeof(uint64_t));
uint64_t v{v1 | v2}; // We are only interested in these bits: 1000 1000
// 1000 1000 .... etc
if ((v & 0x8080808080808080) ==
0) { // if NONE of these are set, e.g. all of them are zero, then
// everything is ASCII
size_t final_pos = pos + 16;
while (pos < final_pos) {
*latin_output++ = char(buf[pos]);
pos++;
}
continue;
}
}
// suppose it is not an all ASCII byte sequence
uint8_t leading_byte = data[pos]; // leading byte
if (leading_byte < 0b10000000) {
// converting one ASCII byte !!!
*latin_output++ = char(leading_byte);
pos++;
} else if ((leading_byte & 0b11100000) ==
0b11000000) { // the first three bits indicate:
// We have a two-byte UTF-8
if (pos + 1 >= len) {
return 0;
} // minimal bound checking
if ((data[pos + 1] & 0b11000000) != 0b10000000) {
return 0;
} // checks if the next byte is a valid continuation byte in UTF-8. A
// valid continuation byte starts with 10.
// range check -
uint32_t code_point =
(leading_byte & 0b00011111) << 6 |
(data[pos + 1] &
0b00111111); // assembles the Unicode code point from the two bytes.
// It does this by discarding the leading 110 and 10
// bits from the two bytes, shifting the remaining bits
// of the first byte, and then combining the results
// with a bitwise OR operation.
if (code_point < 0x80 || 0xFF < code_point) {
return 0; // We only care about the range 129-255 which is Non-ASCII
// latin1 characters. A code_point beneath 0x80 is invalid as
// it is already covered by bytes whose leading bit is zero.
}
*latin_output++ = char(code_point);
pos += 2;
} else {
return 0;
}
}
return latin_output - start;
}
inline result convert_with_errors(const char *buf, size_t len,
char *latin_output) {
const uint8_t *data = reinterpret_cast<const uint8_t *>(buf);
size_t pos = 0;
char *start{latin_output};
while (pos < len) {
// try to convert the next block of 16 ASCII bytes
if (pos + 16 <=
len) { // if it is safe to read 16 more bytes, check that they are ascii
uint64_t v1;
::memcpy(&v1, data + pos, sizeof(uint64_t));
uint64_t v2;
::memcpy(&v2, data + pos + sizeof(uint64_t), sizeof(uint64_t));
uint64_t v{v1 | v2}; // We are only interested in these bits: 1000 1000
// 1000 1000...etc
if ((v & 0x8080808080808080) ==
0) { // if NONE of these are set, e.g. all of them are zero, then
// everything is ASCII
size_t final_pos = pos + 16;
while (pos < final_pos) {
*latin_output++ = char(buf[pos]);
pos++;
}
continue;
}
}
// suppose it is not an all ASCII byte sequence
uint8_t leading_byte = data[pos]; // leading byte
if (leading_byte < 0b10000000) {
// converting one ASCII byte !!!
*latin_output++ = char(leading_byte);
pos++;
} else if ((leading_byte & 0b11100000) ==
0b11000000) { // the first three bits indicate:
// We have a two-byte UTF-8
if (pos + 1 >= len) {
return result(error_code::TOO_SHORT, pos);
} // minimal bound checking
if ((data[pos + 1] & 0b11000000) != 0b10000000) {
return result(error_code::TOO_SHORT, pos);
} // checks if the next byte is a valid continuation byte in UTF-8. A
// valid continuation byte starts with 10.
// range check -
uint32_t code_point =
(leading_byte & 0b00011111) << 6 |
(data[pos + 1] &
0b00111111); // assembles the Unicode code point from the two bytes.
// It does this by discarding the leading 110 and 10
// bits from the two bytes, shifting the remaining bits
// of the first byte, and then combining the results
// with a bitwise OR operation.
if (code_point < 0x80) {
return result(error_code::OVERLONG, pos);
}
if (0xFF < code_point) {
return result(error_code::TOO_LARGE, pos);
} // We only care about the range 129-255 which is Non-ASCII latin1
// characters
*latin_output++ = char(code_point);
pos += 2;
} else if ((leading_byte & 0b11110000) == 0b11100000) {
// We have a three-byte UTF-8
return result(error_code::TOO_LARGE, pos);
} else if ((leading_byte & 0b11111000) == 0b11110000) { // 0b11110000
// we have a 4-byte UTF-8 word.
return result(error_code::TOO_LARGE, pos);
} else {
// we either have too many continuation bytes or an invalid leading byte
if ((leading_byte & 0b11000000) == 0b10000000) {
return result(error_code::TOO_LONG, pos);
}
return result(error_code::HEADER_BITS, pos);
}
}
return result(error_code::SUCCESS, latin_output - start);
}
inline result rewind_and_convert_with_errors(size_t prior_bytes,
const char *buf, size_t len,
char *latin1_output) {
size_t extra_len{0};
// We potentially need to go back in time and find a leading byte.
// In theory '3' would be sufficient, but sometimes the error can go back
// quite far.
size_t how_far_back = prior_bytes;
// size_t how_far_back = 3; // 3 bytes in the past + current position
// if(how_far_back >= prior_bytes) { how_far_back = prior_bytes; }
bool found_leading_bytes{false};
// important: it is i <= how_far_back and not 'i < how_far_back'.
for (size_t i = 0; i <= how_far_back; i++) {
unsigned char byte = buf[-static_cast<std::ptrdiff_t>(i)];
found_leading_bytes = ((byte & 0b11000000) != 0b10000000);
if (found_leading_bytes) {
if (i > 0 && byte < 128) {
// If we had to go back and the leading byte is ascii
// then we can stop right away.
return result(error_code::TOO_LONG, 0 - i + 1);
}
buf -= i;
extra_len = i;
break;
}
}
//
// It is possible for this function to return a negative count in its result.
// C++ Standard Section 18.1 defines size_t is in <cstddef> which is described
// in C Standard as <stddef.h>. C Standard Section 4.1.5 defines size_t as an
// unsigned integral type of the result of the sizeof operator
//
// An unsigned type will simply wrap round arithmetically (well defined).
//
if (!found_leading_bytes) {
// If how_far_back == 3, we may have four consecutive continuation bytes!!!
// [....] [continuation] [continuation] [continuation] | [buf is
// continuation] Or we possibly have a stream that does not start with a
// leading byte.
return result(error_code::TOO_LONG, 0 - how_far_back);
}
result res = convert_with_errors(buf, len + extra_len, latin1_output);
if (res.error) {
res.count -= extra_len;
}
return res;
}
} // namespace utf8_to_latin1
} // unnamed namespace
} // namespace scalar
} // namespace simdutf
#endif
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