Function utf8_read_char

crawl-ref/source/json.cc:239–275

* Read a single UTF-8 character starting at @s, * returning the length, in bytes, of the character read. * * This function assumes input is valid UTF-8, * and that there are enough characters in front of @s. */

 * and that there are enough characters in front of @s.
 */
static int utf8_read_char(const char *s, uchar_t *out)
{
    const unsigned char *c = (const unsigned char*) s;

    ASSERT(utf8_validate_cz(s));

    if (c[0] <= 0x7F)
    {
        /* 00..7F */
        *out = c[0];
        return 1;
    }
    else if (c[0] <= 0xDF)
    {
        /* C2..DF (unless input is invalid) */
        *out = ((uchar_t)c[0] & 0x1F) << 6 |
               ((uchar_t)c[1] & 0x3F);
        return 2;
    }
    else if (c[0] <= 0xEF)
    {
        /* E0..EF */
        *out = ((uchar_t)c[0] &  0xF) << 12 |
               ((uchar_t)c[1] & 0x3F) << 6  |
               ((uchar_t)c[2] & 0x3F);
        return 3;
    }
    else
    {
        /* F0..F4 (unless input is invalid) */
        *out = ((uchar_t)c[0] &  0x7) << 18 |
               ((uchar_t)c[1] & 0x3F) << 12 |
               ((uchar_t)c[2] & 0x3F) << 6  |
               ((uchar_t)c[3] & 0x3F);
        return 4;
    }
}

/*
 * Write a single UTF-8 character to @s,