1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
|
#include "unicode.h"
// implementation adopted from src/unicode.cpp
size_t utf8_sequence_length(unsigned char first_byte) {
const size_t lookup[] = { 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 3, 4 };
uint8_t highbits = static_cast<uint8_t>(first_byte) >> 4;
return lookup[highbits];
}
utf8_parse_result parse_utf8_codepoint(std::string_view input, size_t offset) {
if (offset >= input.size()) {
return utf8_parse_result(utf8_parse_result::INCOMPLETE);
}
// ASCII fast path
if (!(input[offset] & 0x80)) {
return utf8_parse_result(utf8_parse_result::SUCCESS, input[offset], 1);
}
// Invalid: continuation byte as first byte
if (!(input[offset] & 0x40)) {
return utf8_parse_result(utf8_parse_result::INVALID);
}
// 2-byte sequence
if (!(input[offset] & 0x20)) {
if (offset + 1 >= input.size()) {
return utf8_parse_result(utf8_parse_result::INCOMPLETE);
}
if ((input[offset + 1] & 0xc0) != 0x80) {
return utf8_parse_result(utf8_parse_result::INVALID);
}
auto result = ((input[offset] & 0x1f) << 6) | (input[offset + 1] & 0x3f);
return utf8_parse_result(utf8_parse_result::SUCCESS, result, 2);
}
// 3-byte sequence
if (!(input[offset] & 0x10)) {
if (offset + 2 >= input.size()) {
return utf8_parse_result(utf8_parse_result::INCOMPLETE);
}
if ((input[offset + 1] & 0xc0) != 0x80 || (input[offset + 2] & 0xc0) != 0x80) {
return utf8_parse_result(utf8_parse_result::INVALID);
}
auto result = ((input[offset] & 0x0f) << 12) | ((input[offset + 1] & 0x3f) << 6) | (input[offset + 2] & 0x3f);
return utf8_parse_result(utf8_parse_result::SUCCESS, result, 3);
}
// 4-byte sequence
if (!(input[offset] & 0x08)) {
if (offset + 3 >= input.size()) {
return utf8_parse_result(utf8_parse_result::INCOMPLETE);
}
if ((input[offset + 1] & 0xc0) != 0x80 || (input[offset + 2] & 0xc0) != 0x80 || (input[offset + 3] & 0xc0) != 0x80) {
return utf8_parse_result(utf8_parse_result::INVALID);
}
auto result = ((input[offset] & 0x07) << 18) | ((input[offset + 1] & 0x3f) << 12) | ((input[offset + 2] & 0x3f) << 6) | (input[offset + 3] & 0x3f);
return utf8_parse_result(utf8_parse_result::SUCCESS, result, 4);
}
// Invalid first byte
return utf8_parse_result(utf8_parse_result::INVALID);
}
|
