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