private static List <State> GetStates(ReverseWindowReader data, int address)
{
var states = new List <State> {
new State {
Command = new Command {
Simple = true, Value = data[address], CopySize = 1
},
Address = address
}
};
for (int offset = 1; offset <= RingSize; offset++)
{
var cmd = TestCandidate(data, address, address - offset);
if (cmd != null)
{
states.Add(new State {
Command = cmd, Address = address
});
}
}
return(states);
}
private static Command TestCandidate(ReverseWindowReader data, int targetAddress, int sourceAddress)
{
if (data[targetAddress] != data[sourceAddress])
{
return(null);
}
var target = data.Branch(targetAddress);
var source = data.Branch(sourceAddress);
var count = 0;
while (count < MaxCopySize)
{
if (target.Byte() != source.Byte())
{
break;
}
count++;
}
if (count < MinCopySize)
{
return(null);
}
return(new Command {
Simple = false,
CopySize = count,
Address = (sourceAddress - count + 1 + StartWriteAddress) % RingSize
});
}
public static byte[] CompressMax(byte[] target)
{
if (target == null)
{
throw new ArgumentNullException(nameof(target));
}
var data = new ReverseWindowReader(target, 0);
var states = new State[target.Length];
for (int i = 0; i < target.Length; i++)
{
var candidates = GetStates(data, i);
State best = null;
foreach (var current in candidates)
{
if (current.NextAddress < 0)
{
current.PathLength = current.Size;
}
else
{
// TODO: not checking states[] access for null because we want it to throw exception
current.PathLength = states[current.NextAddress].PathLength + current.Size;
}
if ((best == null) || (current.PathLength < best.PathLength))
{
best = current;
}
}
states[i] = best;
}
var step = states[states.Length - 1];
var commands = new List <Command> {
step.Command
};
while (step.NextAddress >= 0)
{
step = states[step.NextAddress];
commands.Add(step.Command);
}
return(CommandsToBytes(commands));
}
public static byte[] Compress(byte[] target)
{
if (target == null)
{
throw new ArgumentNullException(nameof(target));
}
var commands = new List <Command>();
var address = target.Length - 1;
var data = new ReverseWindowReader(target, address);
while (address >= 0)
{
Command cmd = null;
var offset = 1;
while ((offset <= RingSize) && (cmd == null || cmd.CopySize < MaxCopySize))
{
var testCommand = TestCandidate(data, address, address - offset);
if ((testCommand != null) && ((cmd == null) || (testCommand.CopySize > cmd.CopySize)))
{
cmd = testCommand;
}
offset++;
}
if (cmd == null)
{
cmd = new Command {
Simple = true, Value = data[address]
};
address--;
}
else
{
address -= cmd.CopySize;
}
commands.Add(cmd);
}
return(CommandsToBytes(commands));
}
