protected T ReadDictionary(T dictionary, CompactFontFormatData data, string[] stringIndex)
{
while (data.CanRead())
{
operands.Clear();
var infiniteLoopProtection = 0;
while (true)
{
infiniteLoopProtection++;
// Avoid the library getting caught in an infinite loop, probably not possible.
// "An operator may be preceded by up to a maximum of 48 operands."
if (infiniteLoopProtection > 256)
{
throw new InvalidOperationException("Got caught in an infinite loop trying to read a CFF dictionary.");
}
var byte0 = data.ReadByte();
// Operands and operators are distinguished by the first byte, 0 - 21 specify operators
if (byte0 <= 21)
{
var key = byte0 == 12 ? new OperandKey(byte0, data.ReadByte()) : new OperandKey(byte0);
ApplyOperation(dictionary, operands, key, stringIndex);
break;
}
/*
* b0 value value range calculation
* 32 - 246 -107 - +107 b0 - 139
* 247 - 250 +108 - +1131 (b0 - 247)*256 + b1 + 108
* 251 - 254 -1131 - -108 -(b0 - 251)*256 - b1 - 108
* 28 -32768 - +32767 b1 << 8 | b2
* 29 -(2^31)-+(2^31-1) b1 << 24 | b2 << 16 | b3 << 8 | b4
*
* A byte value of 30 defines a real number operand
*/
if (byte0 == 28)
{
var value = data.ReadByte() << 8 | data.ReadByte();
operands.Add(new Operand(value));
}
else if (byte0 == 29)
{
var value = data.ReadByte() << 24 | data.ReadByte() << 16 |
data.ReadByte() << 8 | data.ReadByte();
operands.Add(new Operand(value));
}
else if (byte0 == 30)
{
var realNumber = ReadRealNumber(data);
operands.Add(new Operand(realNumber));
}
else if (byte0 >= 32 && byte0 <= 246)
{
var value = byte0 - 139;
operands.Add(new Operand(value));
}
else if (byte0 >= 247 && byte0 <= 250)
{
var value = (byte0 - 247) * 256 + data.ReadByte() + 108;
operands.Add(new Operand(value));
}
else if (byte0 >= 251 && byte0 <= 254)
{
var value = -(byte0 - 251) * 256 - data.ReadByte() - 108;
operands.Add(new Operand(value));
}
else
{
throw new InvalidOperationException($"The first dictionary byte was not in the range 29 - 254. Got {byte0}.");
}
}
}
return(dictionary);
}