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Fix and optimize LZ77 compression.

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This commit is contained in:
BtbN
2019-04-14 22:29:15 +02:00
parent dda5057d5d
commit 59f0600cc3
2 changed files with 27 additions and 45 deletions
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59
eAmuseCore/Compression/LZ77.cs
View File

@@ -2,16 +2,17 @@
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace eAmuseCore.Compression
{
class RingBuffer
public class RepeatingRingBuffer
{
private byte[] buf;
private int pos;
private int mod;
public RingBuffer(int size)
public RepeatingRingBuffer(int size)
{
if (size == 0 || (size & (size - 1)) != 0)
throw new ArgumentException("Size is not a power of two.", "size");
@@ -40,7 +41,12 @@ namespace eAmuseCore.Compression
public IEnumerable<byte> Slice(int start, int end)
{
for (int i = start; i < end; ++i)
yield return this[i];
{
if (start < 0 && i >= 0)
yield return this[start + (i % start)];
else
yield return this[i];
}
}
}
@@ -50,7 +56,7 @@ namespace eAmuseCore.Compression
public static IEnumerable<byte> Decompress(IEnumerable<byte> data)
{
RingBuffer buffer = new RingBuffer(0x1000);
RepeatingRingBuffer buffer = new RepeatingRingBuffer(0x1000);
int state = 0;
using (var iter = data.GetEnumerator())
@@ -100,7 +106,7 @@ namespace eAmuseCore.Compression
public int length;
}
private static Match findLongestMatch(RingBuffer data, int prefetchLength, int windowSize)
private static Match findLongestMatch(RepeatingRingBuffer data, int prefetchLength, int windowSize, int minLength)
{
Match res = new Match
{
@@ -108,32 +114,23 @@ namespace eAmuseCore.Compression
length = -1
};
for (int j = 2 - prefetchLength; j < 0; ++j)
minLength = Math.Min(1, minLength);
for (int j = 0; j >= minLength - prefetchLength; --j)
{
var sub = data.Slice(-prefetchLength, j);
int subLength = j + prefetchLength;
if (subLength <= res.length)
continue;
for (int i = -prefetchLength - windowSize; i < -prefetchLength; i++)
for (int distance = 1; distance < windowSize - prefetchLength; ++distance)
{
var slice = Enumerable.Empty<byte>();
int dist = -prefetchLength - i;
int start = -prefetchLength - distance;
var match = data.Slice(start, start + subLength);
var repSlice = data.Slice(i, -prefetchLength);
for (int reps = subLength / dist; reps > 0; --reps)
slice = slice.Concat(repSlice);
var match = slice.Concat(data.Slice(i, i + (subLength % dist)));
if (match.ToArray() == sub)
if (match.SequenceEqual(sub))
{
res.distance = dist;
res.distance = distance;
res.length = subLength;
Console.WriteLine("match: " + res.distance + ":" + res.length);
var a = match.ToArray();
if (a != sub)
Console.WriteLine("FALSE!");
return res;
}
}
}
@@ -141,7 +138,7 @@ namespace eAmuseCore.Compression
return res;
}
public static IEnumerable<byte> Compress(IEnumerable<byte> data, int windowSize = 32, int lookAhead = 0xf + minLength)
public static IEnumerable<byte> Compress(IEnumerable<byte> data, int windowSize = 256, int lookAhead = 0xf + minLength)
{
if (lookAhead < 3 || lookAhead > 0xf + minLength)
throw new ArgumentException("lookAhead out of range", "lookAhead");
@@ -150,10 +147,10 @@ namespace eAmuseCore.Compression
if ((windowSize & (windowSize - 1)) != 0)
throw new ArgumentException("windowSize is not a power of two.", "windowSize");
windowSize = Math.Min(windowSize, 0xfff);
windowSize = Math.Min(windowSize, 0x1000);
int prefetchLenght = 0;
RingBuffer inputQueue = new RingBuffer(windowSize);
RepeatingRingBuffer inputQueue = new RepeatingRingBuffer(windowSize);
Queue<byte> outputQueue = new Queue<byte>();
Queue<byte> state = new Queue<byte>();
bool finished = false;
@@ -162,7 +159,7 @@ namespace eAmuseCore.Compression
{
while (true)
{
while (prefetchLenght <= lookAhead && iter.MoveNext())
while (prefetchLenght < lookAhead && iter.MoveNext())
{
inputQueue.Append(iter.Current);
prefetchLenght += 1;
@@ -177,14 +174,14 @@ namespace eAmuseCore.Compression
}
else
{
Match match = findLongestMatch(inputQueue, prefetchLenght, windowSize);
Match match = findLongestMatch(inputQueue, prefetchLenght, windowSize, minLength);
if (match.length >= minLength && match.distance > 0)
{
prefetchLenght -= match.length;
match.length -= minLength;
if (match.length > 0xf || match.distance > 0xfff)
throw new Exception("INTERNAL ERROR: found match is too long!");
if (match.length > 0xf || match.distance > 0xfff || prefetchLenght < 0)
throw new Exception("INTERNAL ERROR: found match is invalid!");
state.Enqueue(0);
outputQueue.Enqueue((byte)(match.distance >> 4));
@@ -204,8 +201,6 @@ namespace eAmuseCore.Compression
foreach (byte b in outputQueue)
yield return b;
Console.WriteLine("state: " + state.Select((b, i) => b << i).Sum());
state.Clear();
outputQueue.Clear();
}

13
eAmuseTest/Program.cs
View File

@@ -43,19 +43,6 @@ namespace eAmuseTest
Console.WriteLine("Ok go");
var rawData = LZ77.Decompress(decryptedData).ToArray();
Console.WriteLine(BytesToString(rawData));
Console.WriteLine("Ok go again");
var recompressed = LZ77.Compress(rawData).ToArray();
Console.WriteLine(BytesToString(recompressed));
Console.WriteLine("Ok ungo");
var redecompressed = LZ77.Decompress(recompressed).ToArray();
Console.WriteLine(BytesToString(redecompressed));
}
private static string BytesToString(IEnumerable<byte> bytes)