/// <summary>Processes numeric escaped chars to find out if they are a control character.</summary>
/// <param name="ch">a char</param>
/// <returns>Returns the char directly or as replacement for the escaped sequence.</returns>
private char ProcessChar(char ch)
{
switch (_state)
{
case StateStart:
{
if (ch == '&')
{
_state = StateAmp;
}
return ch;
}
case StateAmp:
{
_state = ch == '#' ? StateHash : StateError;
return ch;
}
case StateHash:
{
if (ch == 'x')
{
_control = 0;
_digits = 0;
_state = StateHex;
}
else
{
if ('0' <= ch && ch <= '9')
{
_control = ch - '0';
_digits = 1;
_state = StateDig1;
}
else
{
_state = StateError;
}
}
return ch;
}
case StateDig1:
{
if ('0' <= ch && ch <= '9')
{
_control = _control*10 + (ch - '0');
_digits++;
_state = _digits <= 5 ? StateDig1 : StateError;
}
else
{
// sequence too long
if (ch == ';' && Utils.IsControlChar((char)_control))
{
_state = StateStart;
return (char)_control;
}
_state = StateError;
}
return ch;
}
case StateHex:
{
if (('0' <= ch && ch <= '9') || ('a' <= ch && ch <= 'f') || ('A' <= ch && ch <= 'F'))
{
_control = _control*16 + Convert.ToInt32(ch.ToString(), fromBase: 16);
_digits++;
_state = _digits <= 4 ? StateHex : StateError;
}
else
{
// sequence too long
if (ch == ';' && Utils.IsControlChar((char)_control))
{
_state = StateStart;
return (char)_control;
}
_state = StateError;
}
return ch;
}
case StateError:
{
_state = StateStart;
return ch;
}
default:
{
// not reachable
return ch;
}
}
}
