unchecked utf-8 decoding

utf8.cpp

typedef unsigned int Codepoint; // any unsigned int > 21 bits

Codepoint getcp(const char* &c){
    if(*c == 0)return 0;
    Codepoint cp = static_cast<Codepoint>(*c++) & 0xff;  // works for signed or unsigned chars
    if(cp < 0x80)goto onebyte;
    if(cp < 0xe0){ cp &= 0x1f; goto twobyte; }
    if(cp < 0xf0){ cp &= 0x0f; goto threebyte; }
    cp &= 0x07;
    cp = (cp << 6) + (*c++ & 0x3f);
threebyte:
    cp = (cp << 6) + (*c++ & 0x3f);
twobyte:
    cp = (cp << 6) + (*c++ & 0x3f);
onebyte:
    return cp;
}