function isFullWidth(c) {
        if (c < 0x1100)
            return false;
        return c >= 0x1100 && c <= 0x115F ||
               c >= 0x11A3 && c <= 0x11A7 ||
               c >= 0x11FA && c <= 0x11FF ||
               c >= 0x2329 && c <= 0x232A ||
               c >= 0x2E80 && c <= 0x2E99 ||
               c >= 0x2E9B && c <= 0x2EF3 ||
               c >= 0x2F00 && c <= 0x2FD5 ||
               c >= 0x2FF0 && c <= 0x2FFB ||
               c >= 0x3000 && c <= 0x303E ||
               c >= 0x3041 && c <= 0x3096 ||
               c >= 0x3099 && c <= 0x30FF ||
               c >= 0x3105 && c <= 0x312D ||
               c >= 0x3131 && c <= 0x318E ||
               c >= 0x3190 && c <= 0x31BA ||
               c >= 0x31C0 && c <= 0x31E3 ||
               c >= 0x31F0 && c <= 0x321E ||
               c >= 0x3220 && c <= 0x3247 ||
               c >= 0x3250 && c <= 0x32FE ||
               c >= 0x3300 && c <= 0x4DBF ||
               c >= 0x4E00 && c <= 0xA48C ||
               c >= 0xA490 && c <= 0xA4C6 ||
               c >= 0xA960 && c <= 0xA97C ||
               c >= 0xAC00 && c <= 0xD7A3 ||
               c >= 0xD7B0 && c <= 0xD7C6 ||
               c >= 0xD7CB && c <= 0xD7FB ||
               c >= 0xF900 && c <= 0xFAFF ||
               c >= 0xFE10 && c <= 0xFE19 ||
               c >= 0xFE30 && c <= 0xFE52 ||
               c >= 0xFE54 && c <= 0xFE66 ||
               c >= 0xFE68 && c <= 0xFE6B ||
               c >= 0xFF01 && c <= 0xFF60 ||
               c >= 0xFFE0 && c <= 0xFFE6;
    }
Returns the width of a tab character at screenColumn.