Support cache file reading from path.

Until now we could only read cache file by providing cache hint and
quantization type. This commit adds static method which can read any
valid cache file from file.

src/main/java/azgracompress/cache/ICacheFile.java

@@ -10,6 +10,8 @@ public interface ICacheFile {
 
     void readFromStream(DataInputStream inputStream) throws IOException;
 
+    void readFromStream(DataInputStream inputStream, CacheFileHeader header) throws IOException;
+
     CacheFileHeader getHeader();
 
     void report(StringBuilder builder);

src/main/java/azgracompress/cache/QuantizationCacheManager.java

@@ -36,7 +36,7 @@ public class QuantizationCacheManager {
     private File getCacheFilePathForSQ(final String trainFile, final int codebookSize) {
         final File inputFile = new File(trainFile);
         return new File(cacheFolder, String.format("%s_%d_bits.qvc",
-                inputFile.getName(), codebookSize));
+                                                   inputFile.getName(), codebookSize));
     }
 
     /**
@@ -52,7 +52,7 @@ public class QuantizationCacheManager {
                                        final V3i vDim) {
         final File inputFile = new File(trainFile);
         return new File(cacheFolder, String.format("%s_%d_%dx%dx%d.qvc", inputFile.getName(), codebookSize,
-                vDim.getX(), vDim.getY(), vDim.getZ()));
+                                                   vDim.getX(), vDim.getY(), vDim.getZ()));
     }
 
 
@@ -143,8 +143,8 @@ public class QuantizationCacheManager {
      */
     public String saveCodebook(final String trainFile, final VQCodebook codebook) throws IOException {
         final String fileName = getCacheFilePathForVQ(trainFile,
-                codebook.getCodebookSize(),
-                codebook.getVectorDims()).getAbsolutePath();
+                                                      codebook.getCodebookSize(),
+                                                      codebook.getVectorDims()).getAbsolutePath();
 
         final CacheFileHeader header = createHeaderForVQ(new File(trainFile).getName(), codebook);
         final VQCacheFile cacheFile = new VQCacheFile(header, codebook);
@@ -282,6 +282,21 @@ public class QuantizationCacheManager {
         return null;
     }
 
+    public static ICacheFile readCacheFile(final String path) {
+        try (FileInputStream fis = new FileInputStream(path);
+             DataInputStream dis = new DataInputStream(fis)) {
+            CacheFileHeader header = new CacheFileHeader();
+            header.readFromStream(dis);
+
+            ICacheFile cacheFile = getCacheFile(header.getQuantizationType());
+            assert (cacheFile != null);
+            cacheFile.readFromStream(dis, header);
+            return cacheFile;
+        } catch (IOException e) {
+            return null;
+        }
+    }
+
     /**
      * Inspect cache file specified by the path.
      *

src/main/java/azgracompress/cache/SQCacheFile.java

@@ -5,8 +5,6 @@ import azgracompress.quantization.scalar.SQCodebook;
 import java.io.DataInputStream;
 import java.io.DataOutputStream;
 import java.io.IOException;
-import java.util.Arrays;
-import java.util.stream.Collectors;
 
 public class SQCacheFile implements ICacheFile {
     private CacheFileHeader header;
@@ -36,9 +34,11 @@ public class SQCacheFile implements ICacheFile {
 
     public void readFromStream(DataInputStream inputStream) throws IOException {
         header = new CacheFileHeader();
-
         header.readFromStream(inputStream);
+        readFromStream(inputStream, header);
+    }
 
+    public void readFromStream(DataInputStream inputStream, CacheFileHeader header) throws IOException {
         final int codebookSize = header.getCodebookSize();
         final int[] centroids = new int[codebookSize];
         final long[] frequencies = new long[codebookSize];

src/main/java/azgracompress/cache/VQCacheFile.java

@@ -38,9 +38,12 @@ public class VQCacheFile implements ICacheFile {
 
     public void readFromStream(DataInputStream inputStream) throws IOException {
         header = new CacheFileHeader();
-
         header.readFromStream(inputStream);
+        readFromStream(inputStream, header);
+    }
 
+    @Override
+    public void readFromStream(DataInputStream inputStream, CacheFileHeader header) throws IOException {
         final int codebookSize = header.getCodebookSize();
         final CodebookEntry[] vectors = new CodebookEntry[codebookSize];
         final long[] frequencies = new long[codebookSize];

src/main/java/azgracompress/quantization/vector/VQCodebook.java

@@ -43,6 +43,16 @@ public class VQCodebook {
         return vectors;
     }
 
+    public int[][] getRawVectors() {
+        assert (codebookSize == vectors.length);
+        assert (vectors[0].getVector().length == (int) vectorDims.multiplyTogether());
+        final int[][] rawCodebook = new int[vectors.length][(int) vectorDims.multiplyTogether()];
+        for (int i = 0; i < codebookSize; i++) {
+            rawCodebook[i] = vectors[i].getVector();
+        }
+        return rawCodebook;
+    }
+
     /**
      * Get frequencies of codebook vectors at indices.
      *