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typedef struct {
    char mask;    /* char data will be bitwise AND with this */
    char lead;    /* start bytes of current char in utf-8 encoded character */
    uint32_t beg; /* beginning of codepoint range */
    uint32_t end; /* end of codepoint range */
    int bits_stored; /* the number of bits from the codepoint that fits in char */
}utf_t;

utf_t * utf[] = {
    /*             mask        lead        beg      end       bits */
    [0] = &(utf_t){0b00111111, 0b10000000, 0,       0,        6    },
    [1] = &(utf_t){0b01111111, 0b00000000, 0000,    0177,     7    },
    [2] = &(utf_t){0b00011111, 0b11000000, 0200,    03777,    5    },
    [3] = &(utf_t){0b00001111, 0b11100000, 04000,   0177777,  4    },
    [4] = &(utf_t){0b00000111, 0b11110000, 0200000, 04177777, 3    },
          &(utf_t){0},
};

uint32_t to_cp(const char chr[4])
{
    int bytes = utf8_len(*chr);
    int shift = utf[0]->bits_stored * (bytes - 1);
    uint32_t codep = (*chr++ & utf[bytes]->mask) << shift;

    for(int i = 1; i < bytes; ++i, ++chr) {
        shift -= utf[0]->bits_stored;
        codep |= ((char)*chr & utf[0]->mask) << shift;
    }

    return codep;
}

在我看来，循环中的两行应使用utf[i]而不是utf[0]，如下所示：

        shift -= utf[i]->bits_stored;
        codep |= ((char)*chr & utf[i]->mask) << shift;

对吗？

Answer 1

utf[0]是正确的。该条目适用于所有尾随字节； utf[j]以长度j的顺序描述初始字节。

这个UTF8到代码点的示例正确吗？

1 个答案: