/// <summary>
/// Try to convert a char to a 5-bit Baudot code.
/// </summary>
/// <param name="ch">Char to convert.</param>
/// <param name="result">Baudot code.</param>
/// <param name="shift">Shift in which the char is found.</param>
/// <param name="lsbFirst">Order of the returned code.</param>
/// <returns>Whether the conversion succeeded.</returns>
private static bool TryCharToCode(
char ch, out VBit result, out Shift shift, bool lsbFirst)
{
// Determine whether the char lives in both shifts,
// in the letter shift or otherwise default to the figure shift.
switch (ch)
{
case '\0':
case '\r':
case '\n':
case ' ':
shift = Shift.Both;
break;
default:
shift = (ch >= 65 && ch <= 90) ?
Shift.Letter :
Shift.Figure;
break;
}
// Check if we can lookup the char in the "main"
// lookup array.
if (ch < Constants.LsbFirstCodeLookup.Length
// These arrays have the same length...
//&& ch < Constants.MsbFirstCodeLookup.Length
)
{
byte temp = (lsbFirst) ?
Constants.LsbFirstCodeLookup[ch] :
Constants.MsbFirstCodeLookup[ch];
// If temp is 255 the char is found in the lookup
// array but is not a baudot supported character.
result = (temp == 0xFF) ?
new VBit() :
(VBit)temp;
return(temp != 0xFF);
}
// Check if the char is one of the four
// that are not in main array.
switch (ch)
{
case 'Ю':
result = lsbFirst ?
(VBit)26 :
(VBit)11;
return(true);
}
// Not a supported character.
result = (VBit)0x00;
return(false);
}
/// <summary>
/// Converts a string to Baudot code.
/// </summary>
/// <param name="str">String to convert.
/// Note: lowercase is converted upper,
/// invalid characters are ignored.</param>
/// <param name="lsbFirst">Whether the least significant bit is left.</param>
/// <returns>Enumerable of Baudot codes.</returns>
public static IEnumerable <VBit> ToCode(string str, bool lsbFirst)
{
if (str == null)
{
throw new ArgumentNullException(nameof(str));
}
Contract.Ensures(
Contract.Result <IEnumerable <VBit> >() != null);
// Start in the default Letter Shift.
Shift currentSet = Shift.Letter;
foreach (char ch in str.ToUpper())
{
Shift shift;
VBit code;
if (TryCharToCode(ch, out code, out shift, lsbFirst))
{
// Valid baudot char,
// check if we need to switch shift.
if ((shift != Shift.Both) && (shift != currentSet))
{
VBit shiftCode = (shift == Shift.Figure) ?
Constants.FS :
Constants.LS;
yield return(shiftCode);
currentSet = shift;
}
yield return(code);
}
}
}
