C++: convert between utf8 and unicode

unicode_utf8.cc

wstring UTF8toUnicode(const string& s)
{
    wstring ws;
    wchar_t wc;
    for( int i = 0;i < s.length(); )
    {
        char c = s[i];
        if ( (c & 0x80) == 0 )
        {
            wc = c;
            ++i;
        }
        else if ( (c & 0xE0) == 0xC0 )
        {
            wc = (s[i] & 0x1F) << 6;
            wc |= (s[i+1] & 0x3F);
            i += 2;
        }
        else if ( (c & 0xF0) == 0xE0 )
        {
            wc = (s[i] & 0xF) << 12;
            wc |= (s[i+1] & 0x3F) << 6;
            wc |= (s[i+2] & 0x3F);
            i += 3;
        }
        else if ( (c & 0xF8) == 0xF0 )
        {
            wc = (s[i] & 0x7) << 18;
            wc |= (s[i+1] & 0x3F) << 12;
            wc |= (s[i+2] & 0x3F) << 6;
            wc |= (s[i+3] & 0x3F);
            i += 4;
        }
        else if ( (c & 0xFC) == 0xF8 )
        {
            wc = (s[i] & 0x3) << 24;
            wc |= (s[i] & 0x3F) << 18;
            wc |= (s[i] & 0x3F) << 12;
            wc |= (s[i] & 0x3F) << 6;
            wc |= (s[i] & 0x3F);
            i += 5;
        }
        else if ( (c & 0xFE) == 0xFC )
        {
            wc = (s[i] & 0x1) << 30;
            wc |= (s[i] & 0x3F) << 24;
            wc |= (s[i] & 0x3F) << 18;
            wc |= (s[i] & 0x3F) << 12;
            wc |= (s[i] & 0x3F) << 6;
            wc |= (s[i] & 0x3F);
            i += 6;
        }
        ws += wc;
    }
    return ws;
}

string UnicodeToUTF8( const wstring& ws )
{
    string s;
    for( int i = 0;i < ws.size(); ++i ) 
    {
        wchar_t wc = ws[i];
        if ( 0 <= wc && wc <= 0x7f )
        {
            s += (char)wc;
        }
        else if ( 0x80 <= wc && wc <= 0x7ff )
        {
            s += ( 0xc0 | (wc >> 6) );
            s += ( 0x80 | (wc & 0x3f) );
        }
        else if ( 0x800 <= wc && wc <= 0xffff )
        {
            s += ( 0xe0 | (wc >> 12) );
            s += ( 0x80 | ((wc >> 6) & 0x3f) );
            s += ( 0x80 | (wc & 0x3f) );
        }
        else if ( 0x10000 <= wc && wc <= 0x1fffff )
        {
            s += ( 0xf0 | (wc >> 18) );
            s += ( 0x80 | ((wc >> 12) & 0x3f) );
            s += ( 0x80 | ((wc >> 6) & 0x3f) );
            s += ( 0x80 | (wc & 0x3f) );
        }
        else if ( 0x200000 <= wc && wc <= 0x3ffffff )
        {
            s += ( 0xf8 | (wc >> 24) );
            s += ( 0x80 | ((wc >> 18) & 0x3f) );
            s += ( 0x80 | ((wc >> 12) & 0x3f) );
            s += ( 0x80 | ((wc >> 6) & 0x3f) );
            s += ( 0x80 | (wc & 0x3f) );
        }
        else if ( 0x4000000 <= wc && wc <= 0x7fffffff )
        {
            s += ( 0xfc | (wc >> 30) );
            s += ( 0x80 | ((wc >> 24) & 0x3f) );
            s += ( 0x80 | ((wc >> 18) & 0x3f) );
            s += ( 0x80 | ((wc >> 12) & 0x3f) );
            s += ( 0x80 | ((wc >> 6) & 0x3f) );
            s += ( 0x80 | (wc & 0x3f) );
        }
    }
    return s;
}