Function utf8_len

common/train.cpp:794–798

};

static size_t utf8_len(char src) {
    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>(src) >> 4;
    return lookup[highbits];
}

// mark each byte with its utf8 unit number.
// returns the number of utf8 characters.