complete lz77 compress algorithm

Author: 15045120

build.gradle

@@ -26,7 +26,7 @@ tasks.withType(JavaCompile) { options.encoding = "UTF-8" }
 
 group = 'com.github.myibu'
 archivesBaseName = "algorithm-java"
-version = "1.0.0b"
+version = "1.0.0c"
 
 repositories {
  mavenCentral()

readme.md

@@ -49,7 +49,7 @@ Reference to: [MersenneTwister.pdf](./docs/HoffmanAndGolombCoding.pdf)
 <dependency>
  <groupId>com.github.myibu</groupId>
  <artifactId>algorithm-java</artifactId>
- <version>1.0.0b</version>
+ <version>1.0.0c</version>
 </dependency>
 ```
 

src/main/java/com/github/myibu/algorithm/compress/LZ77Compressor.java

@@ -3,6 +3,8 @@
 import com.github.myibu.algorithm.data.Bits;
 import com.github.myibu.algorithm.endode.GolombEncoder;
 
+import java.math.BigDecimal;
+import java.math.RoundingMode;
 import java.util.*;
 import java.util.stream.Collectors;
 
@@ -74,41 +76,40 @@ public int compress(byte[] in_data, int in_len, byte[] out_data) {
  }
  int llStart = sEnd - 1, rrStart = 0, llEnd = 0, rrEnd = (lp = lEnd);
  int minMatched = 1, minIndex = 0;
- while (llStart >= 0) {
- int matched = 0, left = llStart, right = rrStart;
- while (left >= 0 && right < rrEnd && sBuf[left--] == lWindow[right++]) {
+ for (int i = llStart; i >= 0; i--) {
+ int matched = 0, left = i, right = rrStart;
+ while (left >= llEnd && right < rrEnd && sBuf[left--] == lWindow[right++]) {
  matched++;
  }
  if (matched >= minMatched) {
- minIndex = llStart;
+ minIndex = i;
  minMatched = matched;
  }
- llStart--;
  }
+ int lWindowLen = lWindow.length;
  // only one byte in window, set tuple to (0, 0, lWindow[0])
- if (lWindow.length == 1) {
+ if (lWindowLen == 1) {
  minIndex = 0;
  }
  // matched
  if (minIndex > 0) {
- // 匹配到5个怎么编码
- tuples.add(Arrays.asList( minIndex + 1, minMatched, (int)lWindow[minMatched]));
- sp += (minMatched + 1);
- ip += (minMatched + 1);
+ tuples.add(Arrays.asList( minIndex + 1, minMatched, (minMatched == lWindowLen) ? null : (int)lWindow[minMatched]));
+ sp += ((minMatched == lWindowLen) ? minMatched : (minMatched + 1));
+ ip += ((minMatched == lWindowLen) ? minMatched : (minMatched + 1));
  } else {
  sp++;
  ip++;
  tuples.add(Arrays.asList(0, 0, (int)lWindow[0]));
  }
  if (isDebug) {
- System.out.println("Txt=" + new String() + new String(in_data) + ", SearchBuffer="
+ System.out.println(", SearchBuffer="
  + new StringBuilder(new String(sBuf)).reverse().toString() + ", LookaheadWindow=" + new String(lWindow)
  + " | " + tuples.get(tuples.size()-1)/* + " | " + (char)(tuples.get(tuples.size()-1).get(2).intValue())*/);
  }
  }
  int compressedLen = doEncode(tuples, out_data);
  if (isDebug) {
- System.out.println("after encode: compressed rate=" + (compressedLen * 1.0 / in_len));
+ System.out.println("after encode: compressed rate=" + new BigDecimal(compressedLen * 100.0 / in_len).setScale(2, RoundingMode.HALF_UP) + "%");
  }
  return compressedLen;
  }
@@ -122,8 +123,11 @@ private int doEncode(List<List<Integer>> tuples, byte[] out_data) {
  bits.append(bits1);
  Bits bits2 = encoder.encode(tuple.get(1), l);
  bits.append(bits2);
- Bits bits3 = Bits.ofByte((byte)tuple.get(2).intValue());
- bits.append(bits3);
+ Bits bits3 = new Bits();
+ if (tuple.get(2) != null) {
+ bits3 = Bits.ofByte((byte) tuple.get(2).intValue());
+ bits.append(bits3);
+ }
  if (isDebug) {
  System.out.println(tuple + " encoded result: " + "("+ bits1 + ", "+ bits2 + ", "+ bits3 + ")");
  }
@@ -181,12 +185,16 @@ public int decompress(byte[] in_data, int in_len, byte[] out_data) {
  }
  }
  }
- if (length == -1 || ip+8 > bits.length()) {
+ if (length == -1 ) {
  break;
  }
- int symbol = (int)bits.subBits(ip, ip+8).toByte();
- tuples.add(Arrays.asList(offset, length, symbol));
- ip += 8;
+ if (length != l && ip + 8 <= bits.length()) {
+ int symbol = (int) bits.subBits(ip, ip + 8).toByte();
+ tuples.add(Arrays.asList(offset, length, symbol));
+ ip += 8;
+ } else {
+ tuples.add(Arrays.asList(offset, length, null));
+ }
  }
  if (isDebug) {
  System.out.println("decode tuples=" + tuples);
@@ -197,17 +205,35 @@ public int decompress(byte[] in_data, int in_len, byte[] out_data) {
  private int doDecode(List<List<Integer>> tuples, byte[] out_data) {
  Bits seq = new Bits();
  for (List<Integer> tuple: tuples) {
- int offset = tuple.get(0), length = tuple.get(1), symbol = tuple.get(2);
- Bits sb = Bits.ofByte((byte) symbol);
- if (offset == 0) {
- seq.append(sb);
+ int offset = tuple.get(0), length = tuple.get(1);
+ if (tuple.get(2) != null) {
+ int symbol = tuple.get(2);
+ Bits sb = Bits.ofByte((byte) symbol);
+ if (offset == 0) {
+ seq.append(sb);
+ if (isDebug) {
+ System.out.println(tuple + ", seq=" + new String(seq.toByteArray()));
+ }
+ } else {
+ int start = seq.byteLength() < s ? seq.byteLength() - offset: s - offset;
+ int used = seq.byteLength() < s ? 0 : seq.byteLength() - s;
+ seq.append(seq.subBits((used + start) * 8, (used + start + length) * 8)).append(sb);
+ if (isDebug) {
+ System.out.println(tuple + ", seq=" + new String(seq.toByteArray()));
+ }
+ }
  } else {
  int start = seq.byteLength() < s ? seq.byteLength() - offset: s - offset;
  int used = seq.byteLength() < s ? 0 : seq.byteLength() - s;
- seq.append(seq.subBits((used + start) * 8, (used + start + length) * 8)).append(sb);
-// System.out.println("start=" + start + ", used=" + used + ", length=" + length + ", seq=" + seq);
+ seq.append(seq.subBits((used + start) * 8, (used + start + length) * 8));
+ if (isDebug) {
+ System.out.println(tuple + ", seq=" + new String(seq.toByteArray()));
+ }
  }
  }
+ if (isDebug) {
+ System.out.println("after decode, bits=" + seq);
+ }
  int len = seq.byteLength();
  for (int i = 0; i < len; i++) {
  out_data[i] = seq.getByte(i).toByte();
@@ -222,4 +248,9 @@ private int doDecode(List<List<Integer>> tuples, byte[] out_data) {
  public void setDebug(boolean isDebug) {
  this.isDebug = isDebug;
  }
+
+ public void setSL(int s, int l) {
+ this.s = s;
+ this.l = l;
+ }
 }

src/test/java/com/github/myibu/algorithm/AlgorithmTest.java

@@ -168,15 +168,14 @@ public void testLZFCompressor() {
 
  @Test
  public void testLZ77Compressor() {
- //todo
  String txt = "abracadabradabracadabradabracadabradabracadabradabracadabradabracadabradabracadabradabracadabradabracadabrad";
  byte[] in_data = txt.getBytes(StandardCharsets.UTF_8);
  byte[] out_data = new byte[in_data.length*2];
  Compressor compressor = new LZ77Compressor();
  compressor.setDebug(true);
  int compressed = compressor.compress(in_data, in_data.length, out_data);
  byte[] compressed_data = Arrays.copyOf(out_data, compressed);
- byte[] decompressed_data = new byte[compressed * 2];
+ byte[] decompressed_data = new byte[txt.length()];
  int decompressed = compressor.decompress(compressed_data, compressed, decompressed_data);
  Assert.assertEquals(txt,
  new String(Arrays.copyOf(decompressed_data, decompressed), StandardCharsets.UTF_8));