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#include <stdint.h>
#include "util/utf8.h"
static bool in_range(char x, uint8_t low, uint8_t high) {
uint8_t v = (uint8_t)x;
return low <= v && v <= high;
}
bool is_utf8(const char *string) {
/* Returns true iff the string is 'well-formed', as defined by
* Unicode Standard 15.0.0. See Chapter 3, D92 and Table 3.7.
*
* UTF-8 strings are sequences of code points encoded in one of the
* following ways. The first byte determines the pattern.
*
* 00..7F
* C2..DF 80..BF
* E0 A0..BF 80..BF
* E1..EC 80..BF 80..BF
* ED 80..9F 80..BF
* EE..EF 80..BF 80..BF
* F0 90..BF 80..BF 80..BF
* F1..F3 80..BF 80..BF 80..BF
* F4 80..8F 80..BF 80..BF
*/
uint8_t range_table[9][8] = {
{0x00, 0x7F},
{0xC2, 0xDF, 0x80, 0xBF},
{0xE0, 0xE0, 0xA0, 0xBF, 0x80, 0xBF},
{0xE1, 0xEC, 0x80, 0xBF, 0x80, 0xBF},
{0xED, 0xED, 0x80, 0x9F, 0x80, 0xBF},
{0xEE, 0xEF, 0x80, 0xBF, 0x80, 0xBF},
{0xF0, 0xF0, 0x90, 0xBF, 0x80, 0xBF, 0x80, 0xBF},
{0xF1, 0xF3, 0x80, 0xBF, 0x80, 0xBF, 0x80, 0xBF},
{0xF4, 0xF4, 0x80, 0x8F, 0x80, 0xBF, 0x80, 0xBF},
};
int lengths[9] = {
1, 2, 3, 3, 3, 3, 4, 4, 4
};
while (string[0]) {
bool accept = false;
for (int i = 0; i < 9; i++) {
if (!in_range(string[0], range_table[i][0],
range_table[i][1])) {
continue;
}
for (int j = 1; j < lengths[i]; j++) {
if (!in_range(string[j], range_table[i][2 * j],
range_table[i][2 * j + 1])) {
// Early exit is necessary to avoid
// reading past the null terminator
return false;
}
}
string += lengths[i];
accept = true;
break;
}
if (!accept) {
return false;
}
}
return true;
}
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