utf8.c

static inline size_t Utf8_Fetch(uint32_t *out, const char *s_) 
{
    const unsigned char *s = (const unsigned char*)s_;
    if ((*s & 0xC0) != 0xC0) {
        *out = *s;
        return *s > 0;
    }

    const static size_t clas[32] = {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,0,0,0,0,0,0,0,2,2,2,2,3,3,4,5};
    size_t cl = clas[*s>>3];

    for (size_t i = 1; i < cl; ++i) {
        if ((s[i] & 0xC0) == 0xC0 || (s[i] & 0x80) == 0) {
            *out = s[0];
            return 1;
        }
    }

    switch (cl) {
    case 2: *out = ((s[0]&0x1f)<<6) | (s[1]&0x3f); break;
    case 3: *out = ((s[0]&0xf)<<12) | ((s[1]&0x3f)<<6) | (s[2]&0x3f); break;
    case 4: *out = ((s[0]&0x7)<<18) | ((s[1]&0x3f)<<12) | ((s[2]&0x3f)<<6) | (s[3]&0x3f); break;
    default: *out = s[0]; return 1; // NOTE(skejeton): class 5 invalid, even if possible, just return it raw and map to class 1 (ascii)
    }

    return cl;
}